U.S. patent application number 15/780188 was filed with the patent office on 2018-12-20 for aqueous ink set for inkjet recording and inkjet recording method.
The applicant listed for this patent is DIC Corporation. Invention is credited to Maiko KITADE, Takahiro NIO, Takuji TSUKAMOTO.
Application Number | 20180362791 15/780188 |
Document ID | / |
Family ID | 59056335 |
Filed Date | 2018-12-20 |
United States Patent
Application |
20180362791 |
Kind Code |
A1 |
NIO; Takahiro ; et
al. |
December 20, 2018 |
AQUEOUS INK SET FOR INKJET RECORDING AND INKJET RECORDING
METHOD
Abstract
An aqueous ink set for inkjet recording includes first to n-th
aqueous inks for inkjet recording. Each of the aqueous inks
contains a pigment, water, a surfactant, a binder resin, a urea
compound, and a water-soluble organic solvent (1) having a boiling
point of from 100.degree. C. to 200.degree. C. inclusive and a
vapor pressure at 20.degree. C. of 0.5 hPa or more. All the first
to n-th aqueous inks satisfy a specific expression for .gamma.1 and
.gamma.2. .gamma.1 is the surface tension of one of the first to
n-th aqueous inks that is jetted as droplets prior to different
one, and .gamma.2 is the surface tension of the different one that
is jetted as droplets after the one of the first to n-th aqueous
inks.
Inventors: |
NIO; Takahiro; (Saitama,
JP) ; KITADE; Maiko; (Saitama, JP) ;
TSUKAMOTO; Takuji; (Saitama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DIC Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
59056335 |
Appl. No.: |
15/780188 |
Filed: |
December 6, 2016 |
PCT Filed: |
December 6, 2016 |
PCT NO: |
PCT/JP2016/086163 |
371 Date: |
May 30, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09D 11/38 20130101;
B41M 5/00 20130101; C09D 11/322 20130101; B41J 2/01 20130101; C09D
11/40 20130101; B41M 5/0023 20130101; C09D 11/326 20130101 |
International
Class: |
C09D 11/40 20060101
C09D011/40; B41M 5/00 20060101 B41M005/00; B41J 2/01 20060101
B41J002/01; C09D 11/322 20060101 C09D011/322 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 2015 |
JP |
2015-245283 |
Claims
1. An aqueous ink set for inkjet recording comprising first to n-th
aqueous inks for inkjet recording, wherein each of the aqueous inks
contains a water-soluble organic solvent (1), a pigment, a
surfactant, a urea compound, a binder resin, and water, the
water-soluble organic solvent (1) having a boiling point of from
100.degree. C. to 200.degree. C. inclusive and a vapor pressure at
20.degree. C. of 0.5 hPa or more, and wherein all the first to n-th
aqueous inks satisfy the following (a):
-3.ltoreq..gamma.1-.gamma.2.ltoreq.3 [mN/m] (a) where .gamma.1 is
the surface tension of any one of the first to n-th aqueous inks
that is jetted as droplets prior to different one of the first to
n-th aqueous inks, and .gamma.2 is the surface tension of the
different one of the first to n-th aqueous inks that is jetted as
droplets after the any one of the first to n-th aqueous inks.
2. The aqueous ink set for inkjet recording according to claim 1,
wherein each of the aqueous inks further contains propylene glycol
(2) and at least one organic solvent (3) selected from the group
consisting of glycerin, diglycerin, glycerin derivatives, and
diglycerin derivatives.
3. The aqueous ink set for inkjet recording according to claim 1,
wherein each of the aqueous inks further contains, as a pigment
dispersant, a polymer (A) having an anionic group and having a
solubility in water of 0.1 g/100 mL or less, a number average
molecular weight within the range of 1,000 to 6,000, and an acid
value within the range of 40 to 400 mg KOH/g.
4. The aqueous ink set for inkjet recording according to claim 3,
wherein the polymer (A) is represented by general formula (3):
##STR00003## (wherein, in formula (3), A.sup.1 represents an
organic lithium initiator residue, A.sup.2 represents a polymer
block of a monomer having an aromatic ring or a heterocycle,
A.sup.3 represents a polymer block having an anionic group, n
represents an integer of 1 to 5, and B represents an aromatic group
or an alkyl group).
5. The aqueous ink set for inkjet recording according to claim 1,
wherein the water-soluble organic solvent (1) is
3-methoxy-1-butanol or 3-methyl-3 -methoxy-1 -butanol.
6. The aqueous ink set for inkjet recording according to claim 1,
wherein the surfactant is an acetylene-based surfactant or a
silicone-based surfactant.
7. An inkjet recording method for a non-absorptive recording medium
or a low-absorptive recording medium, wherein the inkjet recording
method uses the aqueous ink set for inkjet recording according to
claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to an aqueous ink set for
inkjet recording and to an inkjet recording method.
BACKGROUND ART
[0002] Aqueous pigment inks for inkjet recording can form prints
excellent in lightfastness etc. and are therefore contemplated to
be used for printing on various mediums such as plain paper, coated
paper, art paper, plastic films, metals, and fabrics.
[0003] In particular, with the recent dramatic growth of the
print-on-demand market, there is a need for a technique that allows
high-speed printing of aqueous pigment inks for inkjet recording on
a recording medium and production of high-quality prints comparable
to prints obtained by planography.
[0004] To print high-quality prints at high speed, it is necessary
to reduce bleeding (which may be referred to also as "color
mixing") at boundaries between inks with different hues. For
example, one previously known method for preventing bleeding of
inks is for an ink set used for an image forming device that forms
an image by jetting ink droplets at a pixel density of 650 dpi or
more and a recording speed of 0.5 m.sup.2/min or more. This ink set
is characterized in that the ink set contains ink compositions
including at least an ink composition A and an ink composition B
and satisfies prescribed conditions (see, for example, PTL 1 or PTL
2).
[0005] However, when the above inks are used for high-speed
printing on a non-absorptive recording medium or a low-absorptive
recording medium such as coated paper, art paper, or a plastic
film, bleeding at color boundaries between inks with different hues
cannot be reduced to a practically acceptable level. Therefore, a
high-image quality print may not be obtained.
CITATION LIST
Patent Literature
[0006] PTL 1: Japanese Unexamined Patent Application Publication
No. 2005-335280
[0007] PTL 2: Japanese Unexamined Patent Application Publication
No. 2011-79952
SUMMARY OF INVENTION
Technical Problem
[0008] An object of the present invention is to provide an aqueous
ink set for inkjet recording and an inkjet recording method that
allow the formation of prints with reduced bleeding and color
mixing on non-absorptive recording mediums and low-absorptive
recording mediums such as plastics, metals, coated paper, and art
paper that do not absorb or resist absorbing solvents such as
water.
Solution to Problem
[0009] The present inventors have achieved the above object by
providing an ink set which uses inks each containing a urea
compound and a water-soluble organic solvent having a specific
boiling point and a specific vapor pressure and in which the
surface tensions of the inks used in the set are specified.
[0010] Accordingly, the present invention relates to an aqueous ink
set for inkjet recording including first to n-th aqueous inks for
inkjet recording, wherein each of the aqueous inks contains a
water-soluble organic solvent (1), a pigment, a surfactant, a urea
compound, a binder resin, and water, the water-soluble organic
solvent (1) having a boiling point of from 100.degree. C. to
200.degree. C. inclusive and a vapor pressure at 20.degree. C. of
0.5 hPa or more, and wherein all the first to n-th aqueous inks
satisfy the following (a):
[Math. 1]
-3.ltoreq..gamma.1-.gamma.2.ltoreq.3 [mN/m] (a)
where .gamma.1 is the surface tension of any one of the first to
n-th aqueous inks that is jetted as droplets prior to different one
of the first to n-th aqueous inks, and .gamma.2 is the surface
tension of the different one of the first to n-th aqueous inks that
is jetted as droplets after the any one of the first to n-th
aqueous inks.
[0011] The present invention also relates to an inkjet recording
method used for a non-absorptive recording medium or a
low-absorptive recording medium, wherein the inkjet recording
method uses the aqueous ink set for inkjet recording.
Advantageous Effects of Invention
[0012] The use of the aqueous ink set for inkjet recording
according to the present invention allows the production of prints
with reduced bleeding and color mixing on non-absorptive recording
mediums and low-absorptive recording mediums such as plastics,
metals, coated paper, and art paper that do not absorb or resist
absorbing solvents such as water.
Description of Embodiments
[0013] (First to n-th Inks)
[0014] The aqueous ink set for inkjet recording according to the
present invention includes first to n-th aqueous inks.
[0015] The first to n-th inks are aqueous inks for inkjet
recording.
[0016] In the inkjet recording method, an inkjet printer is
generally used. A plurality of inks that differ in at least one of
hue, lightness, and chroma may be installed in the inkjet
printer.
[0017] The first to n-th aqueous inks used may be a combination of
aqueous inks that differ in any one of hue, lightness, and
chroma.
[0018] The first to n-th aqueous inks used may be a combination of
aqueous inks that are equal in hue, lightness, and chroma but
differ in tinting power (specifically a dark ink and a light ink).
Specifically, the aqueous inks used can be, for example, a
combination of inks that contain the same pigment but differ in at
least one of hue, lightness, and chroma.
[0019] Examples of the combination of two of the first to n-th
aqueous inks in the ink set of the present invention include (C, M)
, (C, Y), (C, BK), (M, C), (Y, C), (BK, C), (M, Y) , (Y, M), (M,
BK) , (BK, M), (Y, BK), (BK, Y), (C, LC), (C, LM), (LC, C) , (LM,
C) , (M, LC), (M, LM), (LC, M) , (LM, M), (Y, LC), (Y, LM), (CL,
Y), (LM, Y), (BK, LC), (BK, LM), (LC, BK), (LM, BK), (LC, LM), and
(LM, LC).
[0020] Here, C represents a cyan ink, M represents a magenta ink, Y
represents a yellow ink, BK represents black, LC represents a light
cyan ink, and LM represents a light magenta ink.
(Surface Tension)
[0021] In the aqueous ink set for inkjet recording according to the
present invention, all the first to n-th aqueous inks included in
the ink set satisfy expression (a).
[Math. 2]
-3.ltoreq..gamma.1-65 2.ltoreq.3 [mN/m] (a)
Here, .gamma.1 is the surface tension of any one of the first to
n-th aqueous inks that is jetted as droplets prior to different one
of the first to n-th aqueous inks, and .gamma.2 is the surface
tension of the different one of the first to n-th aqueous inks that
is jetted as droplets after the any one of the first to n-th
aqueous inks.
[0022] Each of the surface tensions .gamma.1 and .gamma.2 means
both dynamic surface tension and static surface tension. In the ink
set of the present invention, inks that satisfy the above
expression (a) are used irrespective of whether each of the surface
tensions .gamma.1 and .gamma.2 is dynamic surface tension or static
surface tension.
[0023] The surface tension of each of the inks in the present
invention at 25.degree. C. is preferably 20 to 50 mN/m and more
preferably 20 to 40 mN/m. This is because the occurrence of
bleeding at color boundaries between inks can be effectively
reduced, because image defects such as feathering can be prevented,
and because the occurrence of ink ejection failure and misdirection
caused by leakage of the inks in the vicinity of nozzles during ink
ejection can be prevented.
[0024] Known examples of the method for measuring static surface
tension include a capillary-rise method, a dropping method, and a
ring method. In the present invention, to measure the static
surface tension, a Wilhelmy method (vertical plate method) is
used.
[0025] In the Wilhelmy method (vertical plate method), a petri dish
is filled with a medium to be measured (such as an ink), and a
probe is brought into contact with the surface of the liquid. Upon
contact with the liquid surface, the probe is pulled into the water
by its surface tension. Let the force when the probe in equilibrium
is pulled into the water be P. Then expression (b) derived from the
Wilhelmy principle holds, and the surface tension is determined. In
expression (b), S is the cross-sectional area of the probe; L is
the circumferential length of the probe; m is the weight of the
probe; h is the amount of sinking; p is the density of the liquid;
and g is the gravitational acceleration (about 9.8 m/s.sup.2).
[Math. 3]
P=mg+L.gamma.-sh.rho.g (b)
[0026] However, the force P when the probe is pulled includes
buoyancy shpg. In practice, h is set to zero so that the buoyancy
is adjusted to zero. Specifically, the probe is pulled up to set h
to zero, and force P.sub.1 when h is zero is measured to determine
the buoyancy .gamma. using (expression c).
[Math. 4]
P.sub.1=mg+L.gamma..gamma.=(P.sub.1-mg)/L (c)
[0027] The range of ".gamma.1-.gamma.2" in expression (a) above is
from -3 to 3 inclusive, as described above. However, it is
preferable to use an ink set in which the range of
".gamma.1-.gamma.2" is from -1 to 1 inclusive. In order to obtain a
print with further reduced bleeding and color mixing on a
non-absorptive recording medium or a low-absorptive recording
mediums, it is particularly preferable to use an ink set in which
the range of ".gamma.1-.gamma.2" is from -0.2 to 0.2 inclusive.
[0028] When first to n-th aqueous inks satisfying the above
expression (a) are used, variations in the amounts (densities) of
surfactants present on the surfaces of aqueous ink droplets landing
on a recording medium tend to be reduced. Therefore, even when two
or more aqueous ink droplets landing on a recording medium are
brought into contact with each other, migration of the ink
components between the aqueous ink droplets due to the difference
in concentration of the surfactants is reduced, so that a print
with reduced bleeding and color mixing may be obtained.
[0029] Each of the above-described aqueous inks contains a specific
water-soluble organic solvent (1) described later and is therefore
excellent in quick-drying characteristics. Since aqueous ink
droplets landing on a recording medium dry and thicken quickly,
spreading of the ink droplets can be minimized. In this case,
migration of the ink components between the aqueous ink droplets is
reduced, so that a print with reduced bleeding and color mixing may
be obtained.
[0030] The phrase "jetting ink droplets" in the present invention
means that the ink is ejected from an ink jet head to cause the ink
droplets to land on a recording medium. The phrase "jetted as
droplets prior to" means that droplets of one of two aqueous inks
selected from the first to n-th aqueous inks are caused to land on
a recording medium prior to droplets of the other aqueous ink. The
phrase "jetted as droplets after" means that, after droplets of one
of two aqueous inks selected from the first to n-th aqueous inks
are caused to land on a recording medium prior to droplets of the
other aqueous ink, the droplets of the other aqueous ink are caused
to land on the recording medium with delay.
[0031] The intervals between droplets jetted are determined by
printing speed, i.e., recording medium feed speed, and the nozzle
pitch of the inkjet head. However, in the present invention, no
particular limitation is imposed on the intervals between droplets
jetted.
[0032] To jet ink droplets, an inkjet recording device including an
inkjet head can be used. The inkjet head used may be an inkjet head
that can eject only one type of ink from the head or an inkjet head
having two or more ink channels and capable of ejecting a plurality
of inks from among the first to n-th aqueous inks.
[0033] The ink set of the present invention includes aqueous inks
for inkjet recording. As the first to n-th aqueous inks included in
the ink set, inks each containing a water-soluble organic solvent
(1), a pigment, a surfactant, a urea compound, a binder resin, and
water are used.
(Water-Soluble Organic Solvent (1))
[0034] As the water-soluble organic solvent (1) included in each
aqueous ink, a water-soluble organic solvent having a boiling point
of from 100.degree. C. to 200.degree. C. inclusive and a vapor
pressure at 20.degree. C. of 0.5 hPa or more is used.
[0035] The first to n-th aqueous inks each containing the
water-soluble organic solvent (1) are excellent in drying
characteristics after landing on a recording medium. Therefore,
with the obtained aqueous ink set for inkjet recording, prints with
reduced bleeding and color mixing can be formed on a non-absorptive
recording medium or a low-absorptive recording medium.
[0036] The water-soluble organic solvent (1) used may be one or a
combination of two or more from among 3-methoxy-1-butanol,
3-methyl-3-methoxy-1-butanol, 3-methoxy-3-methyl-1-butyl acetate,
ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,
ethylene glycol monopropyl ether, ethylene glycol monobutyl ether,
ethylene glycol monoisobutyl ether, ethylene glycol-t-butyl ether,
propylene glycol monomethyl ether, propylene glycol monoethyl
ether, propylene glycol monopropyl ether, propylene glycol
monomethyl ether acetate, diethylene glycol dimethyl ether,
diethylene glycol methylethyl ether, diethylene glycol diethyl
ether, dipropylene glycol dimethyl ether,
4-methoxy-4-methyl-2-pentanone, and ethyl lactate.
[0037] In particular, from the viewpoint of storage stability of
the first to n-th aqueous inks and their adaptability to components
of an inkjet device, the water-soluble organic solvent (1) used is
preferably a water-soluble organic solvent in which a hydrogen bond
term SH in HSPs (Hansen solubility parameters) is within the range
of 6 to 20. The adaptability to the components of the inkjet device
means deterioration of the inkjet device due to swelling and
dissolution of the components that occur when the inks are in
contact with a head unit and channels of the device for a long
time.
[0038] As the water-soluble organic solvent with an HSP within the
above range, it is preferable to use, for example,
3-methoxy-1-butanol, 3-methyl-3-methoxy-1-butanol, ethylene glycol
monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol
monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol
monoisobutyl ether, ethylene glycol-t-butyl ether, propylene glycol
monomethyl ether, or propylene glycol monoethyl ether, and it is
particularly preferable to use 3-methoxy-1-butanol or
3-methyl-3-methoxy-1-butanol.
[0039] In the present invention, it is preferable to use the
water-soluble organic solvent (1) in combination with propylene
glycol (2) and at least one organic solvent (3) selected from the
group consisting of glycerin, diglycerin, glycerin derivatives, and
diglycerin derivatives because the excellent drying characteristics
of the aqueous inks after landing on a recording medium are not
impaired, because the formation of a coating near ink ejection
nozzles due to drying or solidification of the aqueous inks can be
prevented, and because, even when the coating of an aqueous ink is
formed, the coating can be re-dispersed in the aqueous ink newly
supplied and therefore excellent ejectability can be
maintained.
[0040] Examples of the glycerin derivatives and the diglycerin
derivatives used as the organic solvent (3) include polyglycerin,
diglycerin fatty acid esters, polyoxypropylene(n)polyglyceryl
ethers represented by general formula (1), and
polyoxyethylene(n)polyglyceryl ethers represented by general
formula (2), and two or more of them may be used simultaneously. In
the present invention, it is particularly preferable to select
glycerin or polyoxypropylene(n)polyglyceryl ether with n=8 to
15.
##STR00001##
[0041] In general formulas (1) and (2), m, n, o, and p each
independently represent an integer of 1 to 10.
[0042] The water-soluble organic solvent (1) is used preferably in
an amount within the range of 1 to 20% by mass based on the mass of
each of the first to n-th aqueous inks, more preferably in an
amount within the range of 1 to 15% by mass, and particularly
preferably in an amount within the range of 1 to 10% by mass from
the viewpoint of forming a print with further reduced bleeding and
color mixing on a non-absorptive recording medium or a
low-absorptive recording medium.
[0043] The propylene glycol (2) is used preferably in an amount
within the range of 1 to 30% by mass based on the mass of each of
the first to n-th aqueous inks, more preferably in an amount within
the range of 1 to 25% by mass, and particularly preferably in an
amount within the range of 1 to 20% by mass from the viewpoint of
obtaining inks for inkjet recording having good ejectability
without influence on the quick-drying characteristics of the
inks.
[0044] The organic solvent (3) is used preferably in an amount
within the range of 1 to 20% by mass based on the mass of each of
the first to n-th aqueous inks, more preferably in an amount within
the range of 2 to 18% by mass, and particularly preferably in an
amount within the range of 4 to 15% by mass from the viewpoint of
preventing drying etc. of the aqueous inks near ink ejection
nozzles.
(Pigment)
[0045] No particular limitation is imposed on the pigment used in
the present invention, and organic pigments and inorganic pigments
used for aqueous inks for aqueous inkjet recording may be used. The
pigment used may be an untreated pigment not subjected to surface
treatment for improving dispersibility or a treated pigment
subjected to surface treatment using a synergist such as a pigment
derivative.
[0046] The inorganic pigment used may be, for example, iron oxide,
carbon black, etc. Examples of the carbon black that can be used
include carbon black produced by known methods such as a contact
method, a furnace method, and a thermal method.
[0047] Examples of the organic pigment that can be used include azo
pigments (including azo lakes, insoluble azo pigments, condensed
azo pigments, chelate azo pigments, etc.), polycyclic pigments
(such as phthalocyanine pigments, perylene pigments, perinone
pigments, anthraquinone pigments, quinacridone pigments, dioxazine
pigments, thioindigo pigments, isoindolinone pigments, and
quinophthalone pigments), dye chelates (such as basic dye-type
chelates and acid dye-type chelates), nitro pigments, nitroso
pigments, and aniline black.
[0048] Examples of the pigment used for black inks include: carbon
black manufactured by Mitsubishi Chemical Corporation such as No.
2300, No. 2200B, No. 900, No. 960, No. 980, No. 33, No. 40, No. 45,
No. 45L, No. 52, HCF88, MA7, MA8, and MA100; carbon black
manufactured by Columbian Chemicals Company such as Raven 5750,
Raven 5250, Raven 5000, Raven 3500, Raven 1255, and Raven700;
carbon black manufactured by Cabot Corporation such as Regal 400R,
Regal 330R, Regal 660R, Mogul L, Mogul 700, Monarch 800, Monarch
880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, and
Monarch 1400; and carbon black manufactured by Degussa such as
Color Black FW1, FW2, FW2V, FW18, FW200, S150, S160, and S170,
Printex 35, U, V, and 1400U, Special Black 6, 5, 4, and 4A, NIPEX
150, NIPEX 160, NIPEX 170, and NIPEX 180.
[0049] Specific examples of the pigment used for yellow inks
include C.I. Pigment Yellow 1, 2, 12, 13, 14, 16, 17, 73, 74, 75,
83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 138, 150, 151,
154, 155, 174, 180, and 185.
[0050] Specific examples of the pigment used for magenta inks
include C.I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57:1,
112, 122, 123, 146, 168, 176, 184, 185, 202, 209, 269, and 282 and
C.I. Pigment Violet 19.
[0051] Specific examples of the pigment used for cyan inks include
C.I. Pigment Blue 1, 2, 3, 15, 15:3, 15:4, 16, 22, 60, 63, and
66.
[0052] Specific examples of the pigment used for white inks
include: sulfates and carbonates of alkaline-earth metals; silicas
such as fine silicic acid powder and synthetic silicates; calcium
silicate; alumina; hydrated alumina; titanium oxide; zinc oxide;
talc; and clay. These inorganic white pigments may have been
subjected to surface treatment using various surface treatment
methods.
[0053] When each of the aqueous inks included in the aqueous ink
set for inkjet recording according to the present invention is
produced, it is preferable to use a pigment dispersion in which the
pigment is dispersed in advance in a solvent such as water.
[0054] When the pigment dispersion is used, it is preferable that
the pigment used can be stably dispersed in the solvent.
[0055] The pigment dispersion that can be used is, for example, a
dispersion prepared by dispersing the pigment in a solvent such as
water using a pigment dispersant such as a polymer dispersant, a
surfactant, or a pigment derivative.
[0056] As the pigment dispersible in the solvent, a pigment having
dispersibility-imparting groups (hydrophilic functional groups or a
salt thereof) on its surface may be used.
[0057] The pigment used may be a self-dispersible pigment capable
of dispersing in a solvent including water without the use of the
pigment dispersant.
[0058] The self-dispersible pigment used may be, for example, a
pigment subjected to physical treatment or chemical treatment to
introduce (graft) dispersibility-imparting groups to the surface of
the pigment.
[0059] Examples of the method for subjecting the pigment to
physical treatment or chemical treatment include vacuum plasma
treatment, oxidation treatment with hypohalous acid and/or a
hypohalous acid salt, oxidation treatment with ozone, a wet
oxidation method in which the surface of the pigment is oxidized in
water using an oxidizer, and a method including bonding
p-aminobenzoic acid to the surface of the pigment to thereby bond
carboxyl groups through phenyl groups.
[0060] It is unnecessary that the pigment dispersant for imparting
dispersibility be used for an aqueous ink containing the
self-dispersible pigment. Therefore, foaming caused by the pigment
dispersant is unlikely to occur, and good ejection stability is
obtained. Moreover, since a significant increase in viscosity
caused by the pigment dispersant can be prevented, a larger amount
of the pigment can be contained. This allows the density of
printing to be increased sufficiently, or the ink can be handled
easily.
[0061] A commercial self-dispersible pigment may be used. Examples
of the commercial product include: Microjet CW-1 (tradename,
manufactured by Orient Chemical Industries Co., Ltd.); and
CAB-O-JET 200 and CAB-O-JET 300 (tradenames, manufactured by Cabot
Corporation).
(Surfactant)
[0062] The surfactant is used for the purpose of adjusting the
surface tensions of the first to n-th aqueous inks within the
above-described range. Examples of the surfactant include nonionic
surfactants, anionic surfactants, cationic surfactants, and
amphoteric surfactants. Of these, nonionic surfactants are used
preferably.
[0063] Examples of the anionic surfactants include
alkylbenzenesulfonate, alkylphenylsulfonate,
alkylnaphthalenesulfonate, higher fatty acid salts, sulfates of
higher fatty acid esters, sulfonates of higher fatty acid esters,
sulfates and sulfonates of higher alcohol ethers, higher alkyl
sulfosuccinates, polyoxyethylene alkyl ether carboxylates,
polyoxyethylene alkyl ether sulfates, alkyl phosphates, and
polyoxyethylene alkyl ether phosphates. Specific examples of the
anionic surfactants include dodecylbenzenesulfonate,
isopropylnaphthalenesulfonate, monobutylphenylphenolmonosulfonate,
monobutylbiphenylsulfonate, and dibutylphenylphenoldisulfonate.
[0064] Examples of the nonionic surfactants include polyoxyethylene
alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene
fatty acid esters, sorbitan fatty acid esters, polyoxyethylene
sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid
esters, glycerin fatty acid esters, polyoxyethylene glycerin fatty
acid esters, polyglycerin fatty acid esters, sucrose fatty acid
esters, polyoxyethylene alkyl amines, polyoxyethylene fatty acid
amides, fatty acid alkylolamides, alkyl alkanolamides, acetylene
glycol, oxyethylene adducts of acetylene glycol, and polyethylene
glycol-polypropylene glycol block copolymers. Of these,
polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl
ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl
ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid
esters, polyoxyethylene sorbitan fatty acid esters, fatty acid
alkylolamides, acetylene glycol, oxyethylene adducts of acetylene
glycol, and polyethylene glycol-polypropylene glycol block
copolymers are preferred. It is more preferable to use
acetylene-based surfactants such as acetylene glycol and
oxyethylene adducts of acetylene glycol. This is because the
contact angle of each ink droplet landing on a recording medium can
be reduced, so that a print in which the occurrence of printing
unevenness such as white streaks is prevented can be obtained.
[0065] In addition to the above surfactants, other surfactants may
be used such as: silicone-based surfactants such as polysiloxane
oxyethylene adducts; fluorine-based surfactants such as
perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and
oxyethylene perfluoroalkyl ethers; and bio-surfactants such as
spiculisporic acid, rhamnolipid, and lysolecithin. From the
viewpoint of reducing the contact angle of each ink droplet landing
on a recording medium to thereby obtain a print in which the
occurrence of printing unevenness such as white streaks is reduced,
it is more preferable to use silicone-based surfactants such as
polysiloxane oxyethylene adducts.
[0066] The above surfactants may be used alone or in combination of
two or more. It is preferable to use a surfactant that is prevented
from aggregating or separating in each ink and can be stably
dissolved in the solvent contained in the ink. Specifically, it is
preferable to use a surfactant with an HLB within the range of 3 to
20, and it is more preferable to use a surfactant with an HLB
within the range of 3 to 7. When the surfactant with an HLB within
the range of 3 to 7 is used, it is preferable to use a combination
of the surfactant with an HLB within the range of 3 to 7 and, for
example, an organic solvent (1) that can dissolve the
surfactant.
[0067] The surfactant is used preferably in an amount within the
range of 0.001 to 4% by mass based on the mass of each of the first
to n-th aqueous inks, more preferably in an amount within the range
of 0.001 to 2% by mass, and still more preferably in an amount
within the range of 0.01 to 1.5% by mass from the viewpoint of
obtaining an ink set with which the occurrence of bleeding and
color mixing can be further reduced even when the inks are printed
on a non-absorptive recording medium or a low-absorptive recording
medium.
(Urea Compound)
[0068] Examples of the urea compound used in the present invention
include urea and urea derivatives. Urea and urea derivatives have
high moisturizing capability and can function as a solid humectant.
Therefore, the urea compound can prevent each aqueous ink from
drying or solidifying near ejection nozzles, and good ejectability
of the ink can be maintained.
[0069] When droplets of each aqueous ink containing the urea
compound land on a recording medium, the ink dries rapidly by, for
example, heating. Therefore, even when the ink is printed on a
non-absorptive recording medium or a low-absorptive recording
medium, the occurrence of bleeding and color mixing can be
effectively reduced.
[0070] Examples of the urea derivatives include ethylene urea,
propylene urea, diethylurea, thiourea, N,N-dimethylurea,
hydroxyethylurea, hydroxybutylurea, ethylenethiourea, and
diethylthiourea, and two or more of these may be used
simultaneously.
[0071] Particularly preferably, the urea compound used is urea,
ethylene urea, or 2-hydroxyethylurea because they are easily
dissolved in water and are easily available.
[0072] To improve ink ejectability and drying characteristics of
prints, the content of the urea compound used is preferably in an
amount within the range of 1.0% by mass to 20.0% by mass based on
the mass of each of the first to n-th aqueous inks, more preferably
in an amount within the range of 2.0% by mass to 15.0% by mass, and
still more preferably in an amount within the range of 3.0% by mass
to 10.0% by mass.
[0073] The water-soluble organic solvent (1) and the urea compound
are used preferably in an amount within the range of 1 to 25% by
mass based on the mass of each of the first to n-th aqueous inks,
more preferably in an amount within the range of 3 to 20% by mass,
and particularly preferably in an amount within the range of 5 to
18% by mass because the ink is less likely to adhere to other
mediums even immediately after printing (i.e., is excellent in
fixability).
[0074] When the propylene glycol (2) and the organic solvent (3)
are used, the total mass of the water-soluble organic solvent (1)
used, the urea compound used, the propylene glycol (2), and the
organic solvent (3) is preferably within the range of 20 to 50% by
mass based on the mass of each of the first to n-th aqueous inks,
more preferably within the range of 20 to 40% by mass, and
particularly preferably within the range of 22 to 35% by mass
because the ink is less likely to adhere to other mediums even
immediately after printing (i.e., is excellent in fixability).
(Binder Resin)
[0075] The binder resin used in the present invention may be one or
a combination of two or more from among polyvinyl alcohol, gelatin,
polyethylene oxide, polyvinylpyrrolidone, acrylic resins, urethane
resins, dextran, dextrins, carrageenans (K, t, X, etc.), agar,
pullulan, water-soluble polyvinyl butyral, hydroxyethyl cellulose,
and carboxymethyl cellulose.
[0076] In particular, the binder resin used is preferably an
acrylic resin. Specifically, the binder resin used is preferably an
acrylic resin having an amido group and particularly preferably an
acrylic resin having an amido group and having an alkoxysilyl group
etc. because of good re-dispersibility in the aqueous inks. The
"acrylic resin" means a copolymer containing a monomer having a
(meth)acryloyl group as a raw material.
(Acrylic Resin Having Amido Group)
[0077] The acrylic resin having an amido group has the effect of
improving re-dispersibility of each of the aqueous inks in the
present invention.
[0078] The acrylic resin having an amido group can be obtained, for
example, by polymerizing monomer components including an acrylic
monomer having an amido group. The acrylic monomer having an amido
group is used preferably in an amount within the range of 5% by
mass or less based on the total amount of the monomer components
because better re-dispersibility can be obtained and a print
excellent in rub-fastness is obtained. The acrylic monomer having
an amido group is used preferably in an amount within the range of
0.5% by mass to 5% by mass, more preferably in an amount within the
range of 0.5% by mass to 4% by mass, and particularly preferably in
an amount within the range of 1.5% by mass to 3% by mass.
[0079] Examples of the acrylic monomer having an amido group
include (meth) acrylamide, N-methyl(meth)acrylamide,
N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide,
N-methylol(meth)acrylamide, N-isopropyl(meth)acrylamide,
N-butyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide,
N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide,
N,N-dimethylaminopropyl(meth)acrylamide, diacetone(meth)acrylamide,
and hydroxyethyl(meth)acrylamide.
[0080] Examples of an addition monomer that can be combined with
the acrylic monomer having an amido group include: (meth)acrylic
acid and alkali metal salts thereof; (meth)acrylate-based monomers
such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl
(meth)acrylate, 2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate,
and cyclohexyl (meth)acrylate; and acrylic monomers such as (meth)
acrylonitrile, 2-dimethylaminoethyl (meth)acrylate, and glycidyl
(meth)acrylate.
[0081] Other examples of the additional monomer include: aromatic
vinyl compounds such as styrene, .alpha.-methylstyrene,
p-tert-butylstyrene, vinylnaphthalene, and vinylanthracene;
vinylsulfonic acid compounds such as vinylsulfonic acid and styrene
sulfonic acid; vinylpyridine compounds such as 2-vinylpyridine,
4-vinylpyridine, and naphthylvinylpyridine; vinyltriethoxysilane;
vinyltrimethoxysilane; p-styryltrimethoxysilane;
3-methacryloxypropylmethyldimethoxysilane;
3-methacryloxypropyltrimethoxysilane;
3-methacryloxypropyltrimethoxysilane;
3-methacryloxypropyltriethoxysilane; and
3-acryloxypropyltrimethoxysilane.
[0082] To further improve the affinity for the pigment, the
additional monomer used is preferably a monomer having an aromatic
group such as styrene or benzyl (meth)acrylate.
[0083] Among the above acrylic resins each having an amido group,
an acrylic resin (B) having an amido group and having an
alkoxysilyl group etc. is used preferably because the formation of
a coating near ink ejection nozzles due to drying or solidification
of the aqueous inks can be prevented and because, even when the
coating of an aqueous ink is formed, the coating can be
re-dispersed in the aqueous ink newly supplied and therefore
excellent ejectability can be maintained.
[0084] The acrylic resin (b) can be produced, for example, by
polymerizing the monomer having an amido group and a monomer having
an alkoxysilyl group etc. and referred to generally as a silane
coupling agent.
[0085] Examples of the silane coupling agent having an
ethylenically unsaturated group include monomers having an
ethylenically unsaturated group such as vinyltriethoxysilane,
vinyltrimethoxysilane, p-styryltrimethoxysilane,
3-methacryloxypropylmethyldimethoxysilane,
3-methacryloxypropyltrimethoxysilane,
3-methacryloxypropylmethyldiethoxysilane,
3-methacryloxypropyltriethoxysilane, and
3-acryloxypropyltrimethoxysilane.
[0086] The silane coupling agent having an ethylenically
unsaturated group provides a crosslinked structure to the acrylic
resin (B). The silane coupling agent is used preferably in an
amount within the range of 0.05% by mass to 2% by mass based on the
total amount of the monomers used to produce the acrylic resin (B),
more preferably in an amount within the range of 0.05% by mass to
1.5% by mass, and particularly preferably in an amount within the
range of 0.1% by mass to 1.0% by mass because the strength of a
coating after printing and drying is increased and because the
function of improving the rub-fastness of a print is obtained.
[0087] To improve adhesion of each aqueous ink used in the present
invention to non-absorptive recording mediums and low-absorptive
recording mediums, the acrylic resin may contain a component which
is insoluble in tetrahydrofuran (THF) used as an eluent for
molecular weight measurement by gel permeation chromatography and
therefore whose molecular weight is not easily measured.
[0088] The component insoluble in THF used as the eluent for
molecular weight measurement of the acrylic resin by gel permeation
chromatography can be considered to have a number average molecular
weight of at least 100,000 and a mass average molecular weight of
at least 500,000.
[0089] When each of the aqueous inks used in the present invention
is produced, the acrylic resin described above or an aqueous
dispersion of the acrylic resin may be used.
[0090] Examples of the aqueous dispersion of the acrylic resin
include: a dispersion prepared by dispersing the acrylic resin in
water or a water-soluble solvent with the aid of an emulsifier; and
a dispersion prepared by dispersing an acrylic resin having a
hydrophilic group in a solvent such as water.
[0091] Examples of the emulsifier include: nonionic emulsifiers
such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl
ethers, and polyoxyethylene-polyoxypropylene copolymers; anionic
emulsifiers such as alkyl sulfates, alkyl benzenesulfonates,
polyoxyethylene alkyl ether sulfates, and polyoxyethylene alkyl
phenyl ether sulfates; and cationic emulsifiers such as quaternary
ammonium salt. The emulsifier is used preferably in an amount
within the range of 20 parts by mass or less based on 100 parts by
mass of the acrylic resin and more preferably in an amount within
the range of 5 to 15 parts by mass because a print excellent in
water resistance can be obtained.
[0092] The aqueous dispersion of the acrylic resin can be produced,
for example, by an emulsion polymerization method.
[0093] Examples of the emulsion polymerization method include a
radical emulsion polymerization method using a radical
polymerization initiator.
[0094] Examples of the radical polymerization initiator include:
persulfates such as potassium persulfate, sodium persulfate, and
ammonium persulfate; azo compounds such as
2,2'-azobisisobutyronitrile and dimethyl-2,2'-azobisisobutyrate;
organic peroxides such as benzoyl peroxide and
tert-butylperoxy-2-ethylhexanoate; and redox initiators such as a
combination of an organic peroxide such as cumene hydroperoxide and
a reducing agent such as iron oxide. The amount of the radical
polymerization initiator used is generally preferably within the
range of 0.01 parts by mass to 5 parts by mass and more preferably
within the range of 0.05 parts by mass to 2 parts by mass based on
100 parts by mass of the total mass of the monomers used to produce
the acrylic resin.
[0095] In the emulsion polymerization method, a chain transfer
agent, a pH modifier, etc. may be used if necessary.
[0096] The emulsion polymerization method may be performed in 100
parts by mass to 500 parts by mass of water based on 100 parts by
mass of the total mass of the monomers used to produce the acrylic
resin.
[0097] The emulsion polymerization may be performed in a
temperature range of preferably 5 to 100.degree. C. and more
preferably 50 to 90.degree. C. over 0.1 to 10 hours.
[0098] In an acrylic resin dispersion prepared by dispersing the
acrylic resin having a hydrophilic group in a solvent such as
water, the acrylic resin used may be an acrylic resin having a
hydrophilic group such as an anionic group, a cationic group, or a
nonionic group.
[0099] Examples of the anionic group include a carboxyl group, a
phosphoric acid group, an acidic phosphoric acid ester group, a
phosphorous acid group, a sulfonic acid group, and a sulfinic acid
group, and it is preferable to use any of them after neutralization
with a basic compound.
[0100] Examples of the basic compound used to neutralize the
anionic group include methylamine, dimethylamine, trimethylamine,
ethylamine, diethylamine, triethylamine, 2-aminoethanol,
2-dimethylaminoethanol, ammonia, sodium hydroxide, potassium
hydroxide, tetramethylammonium hydroxide, tetra-n-butylammonium
hydroxide, and trimethylbenzylammonium hydroxide.
[0101] Examples of the cationic group include a primary amino
group, a secondary amino group, a tertiary amino group, and an
ammonium hydroxide group. It is preferable to neutralize these
groups with an acidic compound.
[0102] Examples of the acidic compound used to neutralize the
cationic group include formic acid, acetic acid, propionic acid,
lactic acid, phosphoric acid monomethyl ester, methanesulfonic
acid, benzenesulfonic acid, dodecylbenzenesulfonic acid,
hydrochloric acid, sulfuric acid, and nitric acid.
[0103] Examples of the nonionic group include groups having a
polyether chain such as polyoxyethylene and polyoxypropylene.
[0104] The acrylic resin having a hydrophilic group may be
produced, for example, by polymerizing the monomer having an amido
group, the silane coupling agent, and the monomer having a
hydrophilic group.
[0105] Examples of the monomer having a hydrophilic group include:
acrylic monomers having a carboxyl group such as (meth)acrylic acid
and 2-carboxyethyl (meth)acrylate and alkali metal salts thereof;
tertiary amino group-containing (meth)acrylamides such as
N,N-dimethyl(meth)acrylamide; and tertiary amino group-containing
(meth)acrylates such as dimethylaminoethyl (meth)acrylate and their
quaternized compounds. Of these, (meth)acrylic acid or
dimethylaminoethyl (meth)acrylate is used preferably.
[0106] The dispersion of the acrylic resin having a hydrophilic
group can be produced, for example, by polymerizing the monomers in
an organic solvent to produce the acrylic resin having a
hydrophilic group and then dispersing the acrylic resin in a
solvent such as water.
[0107] The organic solvent used may be one or a combination of two
or more from among: aliphatic and alicyclic hydrocarbons such as
n-hexane, n-heptane, n-octane, cyclohexane, and cyclopentane;
aromatic hydrocarbons such as toluene, xylene, and ethylbenzene;
esters such as ethyl acetate, n-butyl acetate, n-amyl acetate,
ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl
ether acetate, and ethylene glycol monobutyl ether acetate;
alcohols such as methanol, ethanol, iso-propanol, n-butanol,
iso-butanol, ethylene glycol monomethyl ether, ethylene glycol
monoethyl ether, ethylene glycol mono-n-butyl ether, propylene
glycol monomethyl ether, propylene glycol mono-n-propyl ether, and
diethylene glycol monobutyl ether; ketones such as acetone, methyl
ethyl ketone, methyl isobutyl ketone, methyl n-amyl ketone, and
cyclohexanone; ethers such as dimethoxyethane, tetrahydrofuran,
dioxane, ethylene glycol dimethyl ether, ethylene glycol dibutyl
ether, diethylene glycol dimethyl ether, and diethylene glycol
dibutyl ether; N-methylpyrrolidone; dimethylformamide;
dimethylacetamide; and ethylene carbonate.
[0108] As the radical polymerization initiator usable for the
polymerization in the organic solvent, various azo compounds such
as 2,2'-azobis(isobutyronitrile) and
2,2'-azobis(2,4-dimethylvaleronitrile) and various peroxides such
as tert-butyl peroxypivalate, tert-butyl peroxybenzoate, and
tert-butylperoxy-2-ethylhexanoate may be used.
[0109] A preferred method for dispersing the obtained acrylic resin
having a hydrophilic group in an aqueous medium is a phase
inversion emulsification method.
[0110] The phase inversion emulsification method is a method
including: mixing a solvent such as water and an organic solvent
solution of an acrylic resin having a hydrophilic group neutralized
as needed with a basic compound or an acidic compound; and then
dispersing the acrylic resin in the solvent described above
(transfer emulsification). After the phase inversion
emulsification, the organic solvent may be removed if necessary.
During the phase inversion emulsification, an emulsifier may be
used as needed so long as the object of the present invention can
be achieved.
[0111] As the solvent for the acrylic resin dispersion, water, a
water-soluble solvent, or a mixture thereof may be used.
[0112] No particular limitation is imposed on the particle diameter
of the acrylic resin. However, an acrylic resin with a small
diameter is preferred from the viewpoint of ejectability from an
inkjet head. For example, it is preferable to use an acrylic resin
having a volume average particle diameter within the range of 10 to
200 nm as measured using a Microtrac particle size distribution
analyzer "UPA-EX150" manufactured by NIKKISO Co., Ltd.
[0113] The binder resin typified by the acrylic resin is used in an
amount of preferably 3% by mass to 15% by mass (solid content),
more preferably 5% by mass to 12% by mass, and particularly
preferably 7% by mass to 10% by mass based on the mass of each ink,
in order to obtain a print with good gloss and to prevent clogging
of ink ejection nozzles.
(Water)
[0114] Each of the first to n-th aqueous inks included in the ink
set of the present invention contains water. The water is a
dispersion medium for the pigment.
[0115] The water used may be pure water such as ion exchanged
water, ultrafiltrated water, reverse osmotic water, or distilled
water or ultrapure water. The water may be used alone, or a solvent
mixture of water and a water-soluble solvent may be used.
[0116] Examples of the water-soluble solvent include: ketones such
as acetone, methyl ethyl ketone, methyl butyl ketone, and methyl
isobutyl ketone; alcohols such as methanol, ethanol, 2-propanol,
2-methyl-1-propanol, 1-butanol, and 2-methoxyethanol; ethers such
as tetrahydrofuran, 1,4-dioxane, and 1,2-dimethoxyethane; glycols
such as dimethylformamide, N-methylpyrrolidone, ethylene glycol,
diethylene glycol, triethylene glycol, tetraethylene glycol,
polyethylene glycol, and polypropylene glycol; diols such as
butanediol, pentanediol, hexanediol, and similar diols; glycol
esters such as propylene glycol laurate; glycol ethers such as
diethylene glycol monoethyl ether, diethylene glycol monobutyl
ether, diethylene glycol monohexyl ether, propylene glycol ether,
dipropylene glycol ether, and Cellosolves including triethylene
glycol ether; alcohols such as methanol, ethanol, isopropyl
alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, butyl
alcohol, pentyl alcohol, and similar alcohols; sulfolane; lactones
such as .gamma.-butyrolactone; lactams such as
N-(2-hydroxyethyl)pyrrolidone; and other various solvents known as
water-soluble solvents. One or a mixture of two or more of these
water-soluble organic solvents may be used.
(Pigment Dispersant)
[0117] When each of the first to n-th aqueous inks included in the
aqueous ink set for inkjet recording according to the present
invention is produced, a pigment dispersant may be used as needed
for the purpose of improving the dispersion stability of the
pigment.
[0118] No particular limitation is imposed on the pigment
dispersant, and a known polymer dispersant, a known surfactant, or
a pigment derivative may be used.
[0119] The pigment dispersant used may be an aqueous resin, and
preferred examples thereof include: polyvinyl alcohols;
polyvinylpyrrolidones; acrylic resins such as acrylic acid-acrylate
copolymers; styrene-acrylic resins such as styrene-acrylic acid
copolymers, styrene-methacrylic acid copolymers,
styrene-methacrylic acid-acrylate copolymers,
styrene-.alpha.-methylstyrene-acrylic acid copolymers, and
styrene-.alpha.-methylstyrene-acrylic acid-acrylate copolymers;
styrene-maleic acid copolymers; styrene-maleic anhydride
copolymers, vinylnaphthalene-acrylic acid copolymers; and salts of
these aqueous resins. A commercial product can, of course, be used.
Examples of the commercial product that can be used include AJISPER
PB series manufactured by Ajinomoto Fine-Techno Co., Inc.),
Disperbyk series manufactured by BYK-Chemie Japan, EFKA series
manufactured by BASF, SOLSPERSE series manufactured by The Lubrizol
Corporation, and TEGO series manufactured by EVONIK.
[0120] In the present invention, to obtain an ink for inkjet
recording having further improved ejectability, a polymer (A)
described later may be used as the pigment dispersant. In this
case, an ink with the number of coarse particles significantly
reduced can be obtained.
[0121] The polymer (A) used in the present invention is a polymer
having a solubility in water of 0.1 g/100 mL or less and a number
average molecular weight within the range of 1,000 to 6,000 and
having anionic groups. Preferably, the polymer (A) forms fine
particles in water when the degree of neutralization of the anionic
groups with a basic compound is 100%.
[0122] The solubility of the polymer (A) in water is defined as
follows. Sieves with mesh sizes of 250 .mu.m and 90 .mu.m are used
to screen the polymer such that its particle diameter falls within
the range of 250 .mu.m to 90 .mu.m. 0.5 g of the resulting polymer
is sealed in a bag formed from a 400-mesh wire net, immersed in 50
mL of water, and left under mild stirring at a temperature of
25.degree. C. for 24 hours. After immersion for 24 hours, the
400-mesh wire net with the polymer sealed therein is dried in a
dryer set at 110.degree. C. for 2 hours. The change in weight of
the 400-mesh wire net with the polymer sealed therein before and
after the immersion in water is measured, and the solubility is
computed using the following expression.
Solubility (g/100 mL)=(Polymer-sealed 400-mesh wire net before
immersion (g)-Polymer-sealed 400-mesh wire net after immersion
(g)).times.2 [Math. 5]
[0123] In the present invention, whether or not fine particles are
formed in water when the degree of neutralization of the anionic
groups with the basic compound is 100% is judged as follows.
[0124] (1) The acid value of the polymer is measured in advance by
an acid value measurement method according to JIS test method K
0070-1992. Specifically, 0.5 g of the polymer is dissolved in a
tetrahydrofuran (hereinafter may be referred to as THF) solvent,
and titration with a 0.1M alcohol solution of potassium hydroxide
is performed using phenolphthalein as an indicator to determine the
acid value.
[0125] (2) 1 g of the polymer is added to 50 mL of water, and a 0.1
mol/L aqueous potassium hydroxide solution is added in an amount
sufficient to completely neutralize the polymer having the
above-determined acid value to thereby completely neutralize the
polymer.
[0126] (3) The completely neutralized solution is subjected to
ultrasonic waves at a temperature of 25.degree. C. for 2 hours
using an ultrasonic cleaner (ultrasonic cleaner US-102, SND Co.,
Ltd., 38 kHz, self-excited oscillation) and is then left to stand
at room temperature for 24 hours.
[0127] After the solution is left to stand for 24 hours, a sample
solution is sampled at a depth of 2 cm from the surface of the
solution. Then a dynamic light scattering particle size
distribution measurement device (dynamic light scattering particle
size measurement device "Microtrac particle size distribution
analyzer UPA-ST150" manufactured by NIKKISO Co., Ltd.) is used to
determine whether or not information about light scattering due to
the formation of fine particles is obtained, whereby the presence
of fine particles is checked.
[0128] The volume average particle diameter of the fine particles
formed from the polymer (A) used in the present invention is
preferably within the range of 5 nm to 1,000 nm, more preferably
within the range of 7 nm to 700 nm, and particularly preferably
within the range of 10 nm to 500 nm, in order to further improve
the dispersion stability in water.
[0129] As the particle size distribution of the fine particles
becomes narrower, the fine particles tend to exhibit better
dispersibility. However, an embodiment in which the fine particles
have a wide particle size distribution is not excluded. The volume
average particle diameter and the particle size distribution are
measured by the same method as the above-described measurement
method for the fine particles using the dynamic light scattering
particle size distribution measurement device (dynamic light
scattering particle size measurement device "Microtrac particle
size distribution analyzer UPA-ST150" manufactured by NIKKISO Co.,
Ltd.).
(Degree of Neutralization of Polymer (A))
[0130] The degree of neutralization of the polymer (A) used in the
present invention is determined using the following expression.
Degree of neutralization (%)=((Mass (g) of basic
compound).times.56.times.1,000)/(Acid value (mg KOH/g) of polymer
(A).times.Number of equivalents of basic compound.times.mass (g) of
polymer (A)).times.100 [Math. 6]
[0131] The acid value of the polymer (A) is measured according to
JIS test method K 0070-1992. Specifically, 0.5 g of a sample is
dissolved in a THF solvent, and the resulting solution is titrated
with a 0.1M alcoholic solution of potassium hydroxide using
phenolphthalein as an indicator to determine the acid value.
[0132] The acid value of the polymer (A) is preferably 40 to 400 mg
KOH/g, more preferably 40 to 300 mg KOH/g, and most preferably 40
to 190 mg KOH/g.
[0133] The number average molecular weight of the polymer (A) is
preferably 1,000 to 6,000 because good pigment dispersibility is
obtained. The number average molecular weight is more preferably
1,300 to 5,000 and most preferably 1,500 to 4,500.
[0134] In the present invention, the number average molecular
weight is a polystyrene-equivalent value measured by GPC (gel
permeation chromatography) and is specifically a value measured
under the conditions described below.
(Method for Measuring Number Average Molecular Weight (Mn))
[0135] The measurement is performed by gel permeation
chromatography (GPC) under the following conditions.
[0136] Measurement device: High performance GPC ("HLC-8220GPC"
manufactured by TOSOH Corporation)
[0137] Columns: The following columns manufactured by TOSOH
Corporation and connected in series are used.
[0138] "TSKgel G5000" (7.8 mm I.D..times.30 cm).times.1
[0139] "TSKgel G4000" (7.8 mm I.D..times.30 cm).times.1
[0140] "TSKgel G3000" (7.8 mm I.D..times.30 cm).times.1
[0141] "TSKgel G2000" (7.8 mm I.D..times.30 cm).times.1
[0142] Detector: RI (refractive index detector)
[0143] Column temperature: 40.degree. C.
[0144] Eluent: Tetrahydrofuran (THF)
[0145] Flow rate: 1.0 mL/minute
[0146] Injection amount: 100 .mu.L (THF solution with a sample
concentration of 0.4% by mass)
[0147] Standard samples: The following polystyrene standards are
used to produce a calibration curve.
(Polystyrene Standards)
[0148] "TSKgel standard polystyrene A-500" manufactured by TOSOH
Corporation
[0149] "TSKgel standard polystyrene A-1000" manufactured by TOSOH
Corporation
[0150] "TSKgel standard polystyrene A-2500" manufactured by TOSOH
Corporation
[0151] "TSKgel standard polystyrene A-5000" manufactured by TOSOH
Corporation
[0152] "TSKgel standard polystyrene F-1" manufactured by TOSOH
Corporation
[0153] "TSKgel standard polystyrene F-2" manufactured by TOSOH
Corporation
[0154] "TSKgel standard polystyrene F-4" manufactured by TOSOH
Corporation
[0155] "TSKgel standard polystyrene F-10" manufactured by TOSOH
Corporation
[0156] "TSKgel standard polystyrene F-20" manufactured by TOSOH
Corporation
[0157] "TSKgel standard polystyrene F-40" manufactured by TOSOH
Corporation
[0158] "TSKgel standard polystyrene F-80" manufactured by TOSOH
Corporation
[0159] "TSKgel standard polystyrene F-128" manufactured by TOSOH
Corporation
[0160] "TSKgel standard polystyrene F-288" manufactured by TOSOH
Corporation
[0161] "TSKgel standard polystyrene F-550" manufactured by TOSOH
Corporation
[0162] The polymer (A) used is preferably a polymer that is
insoluble or poorly soluble when all the anionic groups are not
neutralized and forms fine particles when all the anionic groups
are neutralized.
[0163] The polymer (A) used may be a polymer having hydrophobic
groups in addition to the hydrophilic anionic groups. Examples of
such a polymer include a block polymer including a polymer block
having hydrophobic groups and a polymer block having anionic
groups.
[0164] As for the number of hydrophobic groups and the number of
anionic groups, it is highly probable that the solubility in water
exceeds 0.1 g/100 mL or fine particles are not formed when the
degree of neutralization of the anionic groups with the basic
compound is 100%. From this point of view, it is preferable that
the number of anionic groups is not so large. In a polymer, the
number of anionic groups and the solubility in water are not
necessarily determined by the acid value of the polymer and the
number of anionic groups in the design phase of the polymer. For
example, among polymers having the same acid value, a polymer
having a low molecular weight tends to have a high solubility in
water, and a polymer having a high molecular weight tends to have a
low solubility in water. Therefore, in the present invention, the
polymer (A) is specified by its solubility in water.
[0165] The polymer (A) may be a homopolymer but is preferably a
copolymer. The polymer (A) may be a random polymer, a block
polymer, or an alternating polymer and is preferably a block
polymer. The polymer may be a branched polymer but is preferably a
linear polymer.
[0166] It is preferable in terms of design flexibility that the
polymer (A) is a vinyl polymer. To produce a vinyl polymer having
the molecular weight and solubility characteristics desired in the
present invention, it is preferable to use a production method
using "living polymerization" such as living radical
polymerization, living cationic polymerization, or living anionic
polymerization.
[0167] In particular, it is preferable that the polymer (A) is a
vinyl polymer produced using a (meth)acrylate monomer as one of the
raw materials. The method for producing such a vinyl polymer is
preferably living radical polymerization or living anionic
polymerization. From the viewpoint that the molecular weight of the
block polymer and each segment thereof can be more precisely
designed, living anionic polymerization is preferred.
[0168] Specifically, as the polymer (A) produced by living anionic
polymerization, a polymer represented by general formula (3) can be
used.
##STR00002##
[0169] In formula (3), A.sup.1 represents an organic lithium
initiator residue, A.sup.2 represents a polymer block of a monomer
having an aromatic ring or a heterocycle, A.sup.3 represents a
polymer block containing an anionic group, n represents an integer
of 1 to 5, and B represents an aromatic group or an alkyl
group.
[0170] In general formula (3), A.sup.1 represents an organic
lithium initiator residue. Specific examples of the organic lithium
initiator include: alkyllithiums such as methyllithium,
ethyllithium, propyllithium, butyllithium (n-butyllithium,
sec-butyllithium, iso-butyllithium, and tert-butyllithium),
pentyllithium, hexyllithium, methoxymethyllithium, and
ethoxymethyllithium; phenylalkylenelithiums such as benzyllithium,
.alpha.-methylstyryllithium, 1,1-diphenyl-3-methylpentyllithium,
1,1-diphenylhexyllithium, and phenylethyllithium; alkenyllithiums
such as vinyllithium, allyllithium, propenyllithium, and
butenyllithium; alkynyllithiums such as ethynyllithium,
butynyllithium, pentynyllithium, and hexynyllithium; aryllithiums
such as phenyllithium and naphthyllithium; heterocyclic lithiums
such as 2-thienyllithium, 4-pyridyllithium, and 2-quinolyllithium;
and alkyl lithium-magnesium complexes such as tri(n-butyl)magnesium
lithium and trimethyl magnesium lithium.
[0171] With the organic lithium initiator, the bond between the
organic group and lithium is cleaved. An active end is thereby
formed in the organic group, and polymerization starts from the
active end. Therefore, the organic group originating from the
organic lithium is bonded to an end of the polymer obtained. In the
present invention, the organic group originating from the organic
lithium and bonded to the end of the polymer is referred to as the
organic lithium initiator residue. For example, in a polymer using
methyllithium as the initiator, the organic lithium initiator acid
group is a methyl group. In a polymer using butyllithium as the
initiator, the organic lithium initiator acid group is a butyl
group.
[0172] In general formula (3) above, A.sup.2 represents a polymer
block having hydrophobic groups. A.sup.2 is a group used for the
purpose of obtaining the appropriate solubility balance balance as
described above and is preferably a group that exhibits high
adsorptive power for the pigment when in contact with the pigment.
From this point of view, A.sup.2 is preferably a polymer block of a
monomer having an aromatic ring or a heterocycle.
[0173] Specifically, the polymer block of a monomer having an
aromatic ring or a heterocycle is a homopolymer or copolymer block
obtained by homopolymerization or copolymerization of a monomer
having an aromatic ring such as a styrene-based monomer or a
monomer having a heterocycle such as a vinylpyridine-based
monomer.
[0174] Examples of the monomer having an aromatic ring include:
styrene-based monomers such as styrene,
p-tert-butyldimethylsiloxystyrene, o-methylstyrene,
p-methylstyrene, p-tert-butylstyrene, p-tert-butoxystyrene,
m-tert-butoxystyrene, p-Cert-(1-ethoxymethyl)styrene,
m-chlorostyrene, p-chlorostyrene, p-fluorostyrene,
.alpha.-methylstyrene, and p-methyl-.alpha.-methylstyrene;
vinylnaphthalene; and vinylanthracene.
[0175] Examples of the monomer having a heterocycle include
vinylpyridine-based monomers such as 2-vinylpyridine and
4-vinylpyridine.
[0176] These monomers may be used alone or as a mixture of two or
more.
[0177] In general formula (3), A.sup.3 represents a polymer block
containing an anionic group. A.sup.3 is used for the purpose of
providing appropriate solubility as described above and for the
purpose of imparting dispersion stability in water when a pigment
dispersion is formed.
[0178] Examples of the anionic group in the polymer block A.sup.3
include a carboxyl group, a sulfonic acid group, and a phosphoric
acid group. Of these, a carboxyl group is preferred because of the
ease of preparation, a wide choice of monomer types, and
availability. Two carboxyl groups in the same molecule or different
molecules may undergo dehydration condensation to thereby form an
acid anhydride group.
[0179] No particular limitation is imposed on the method for
introducing anionic groups into A.sup.3. For example, when the
anionic groups are carboxyl groups, A.sup.3 may be a homopolymer or
copolymer block (PB1) obtained by homopolymerization of
(meth)acrylic acid or copolymerization of (meth)acrylic acid with
another monomer or may be a polymer block (PB2) obtained by
homopolymerizing a (meth)acrylate having a protecting group that
can be reconverted into an anionic group by deprotection or
copolymerizing this (meth)acrylate with another monomer to obtain a
homopolymer or a copolymer and then reconverting part or all of the
protecting groups that can be reconverted into anionic groups into
the anionic groups.
[0180] The (meth)acrylic acid used for the polymer block A.sup.3
means acrylic acid and methacrylic acid, and the (meth)acrylate
means acrylate and methacrylate.
[0181] Specifically, the (meth)acrylate used may be one or a
combination of two or more from among methyl (meth)acrylate, ethyl
(meth)acrylate, iso-propyl (meth)acrylate, allyl (meth)acrylate,
n-butyl (meth)acrylate, iso-butyl (meth)acrylate, sec-butyl
(meth)acrylate, tert-butyl (meth)acrylate, n-amyl (meth)acrylate,
iso-amyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl
(meth)acrylate, 2-ethylhexyl (meth)acrylate, n-lauryl
(meth)acrylate, n-tridecyl (meth)acrylate, n-stearyl
(meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate,
cyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate,
isobornyl (meth)acrylate, tricyclodecanyl (meth)acrylate,
dicyclopentadienyl (meth)acrylate, adamantyl (meth)acrylate,
glycidyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate,
2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate,
dimethylaminoethyl (meth)acrylate, diethylaminoethyl
(meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl
(meth)acrylate, pentafluoropropyl (meth)acrylate, octafluoropentyl
(meth)acrylate, pentadecafluorooctyl (meth)acrylate,
heptadecafluorodecyl (meth)acrylate, N,N-dimethyl(meth)acrylamide,
(meth) acryloylmorpholine, (meth)acrylonitrile, and polyalkylene
oxide group-containing (meth)acrylates such as polyethylene glycol
(meth)acrylate, polypropylene glycol (meth)acrylate, polyethylene
glycol-polypropylene glycol (meth)acrylate, polyethylene
glycol-polybutylene glycol (meth)acrylate, polypropylene
glycol-polybutylene glycol (meth)acrylate, methoxypolyethylene
glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate,
butoxypolyethylene glycol (meth)acrylate, octoxypolyethylene glycol
(meth)acrylate, lauroxypolyethylene glycol (meth)acrylate,
stearoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene
glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate,
and octoxypolyethylene glycol-polypropylene glycol
(meth)acrylate.
[0182] In the living anionic polymerization method, when the
monomer used is a monomer having an active proton-containing group
such as an anionic group, the active end of the living anionic
polymerized polymer immediately reacts with the active
proton-containing group and is thereby deactivated, so that no
polymer is obtained. In living anionic polymerization, it is
difficult to polymerize a monomer having an active
proton-containing group without any treatment. It is therefore
preferable to perform polymerization with the active
proton-containing group protected and then perform deprotection to
reconvert the protecting group into the active proton-containing
group.
[0183] For this reason, it is preferable that a monomer containing
a (meth)acrylate having a protecting group that can be reconverted
into an anionic group by deprotection is used for the polymer block
A.sup.3. The use of such a monomer for the polymerization described
above can prevent inhibition of the polymerization. The anionic
group protected by the protecting group can be reconverted into the
anionic group by deprotection after a block copolymer is
obtained.
[0184] For example, when the anionic group is a carboxyl group, the
carboxyl group is esterified. In a subsequent step, deprotection is
performed through hydrolysis etc., and the esterified group can
thereby be reconverted into the carboxyl group. In this case, the
protecting group that can be converted into the carboxyl group is
preferably a group having an ester bond, and examples of such a
group include: primary alkoxycarbonyl groups such as a
methoxycarbonyl group, an ethoxycarbonyl group, a n-propoxycarbonyl
group, and a n-butoxycarbonyl group; secondary alkoxycarbonyl
groups such as an isopropoxycarbonyl group and a sec-butoxycarbonyl
group; tertiary alkoxycarbonyl groups such as a t-butoxycarbonyl
group; phenylalkoxycarbonyl groups such as a benzyloxycarbonyl
group; and alkoxyalkylcarbonyl groups such as an
ethoxyethylcarbonyl group.
[0185] Examples of the monomer that can be used when the anionic
group is a carboxyl group include: alkyl (meth)acrylates such as
methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl
(meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate,
sec-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl
(meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate,
undecyl (meth)acrylate, dodecyl (meth)acrylate (lauryl
(meth)acrylate), tridecyl (meth)acrylate, pentadecyl
(meth)acrylate, hexadecyl (meth)acrylate, heptadecyl
(meth)acrylate, octadecyl (meth)acrylate (stearyl (meth)acrylate),
nonadecyl (meth)acrylate, and icosanyl (meth)acrylate;
phenylalkylene (meth)acrylates such as benzyl (meth)acrylate; and
alkoxyalkyl (meth)acrylates such as ethoxyethyl (meth)acrylate. One
of these (meth)acrylates (c1) may be used, or a combination of two
or more may be used. Among these (meth)acrylates (c1), t-butyl
(meth)acrylate and benzyl (meth)acrylate are preferably used
because their conversion reaction into a carboxyl group can be
easily performed. In view of industrial availability, t-butyl
(meth)acrylate is more preferred.
[0186] In general formula (3), B represents an aromatic group or an
alkyl group having 1 to 10 carbon atoms. n represents an integer of
1 to 5.
[0187] In the living anionic polymerization method, direct
polymerization of a (meth)acrylate monomer at the active end of a
highly nucleophilic styrene-based polymer may not proceed because
of nucleophilic attack to carbonyl carbon, so that the
(meth)acrylate monomer is not polymerized. Therefore, when the
(meth)acrylate monomer is polymerized to the A.sup.1-A.sup.2
described above, a reaction control agent is used to control
nucleophilicity, and then the (meth)acrylate monomer is
polymerized. B in general formula (3) is a group originating from
the reaction control agent. Specific examples of the reaction
control agent include diphenylethylene, .alpha.-methylstyrene, and
p-methyl-.alpha.-methylstyrene.
(Living Anionic Polymerization Using Microreactor)
[0188] The living anionic polymerization method can be performed as
a batch process used for conventional free radical polymerization
by controlling the reaction conditions. A method in which a
microreactor is used to perform polymerization continuously can
also be used. The microreactor allows a polymerization initiator
and a monomer to be mixed well, so that the reaction starts
simultaneously in the microreactor. In addition, temperature is
uniform within the microreactor, and a uniform polymerization rate
is achieved, so that the polymer produced can have a narrow
molecular weight distribution. In addition, it is easy to produce a
block copolymer in which the components of the blocks are not mixed
with each other because their growing ends are stable. Since the
reaction temperature is well controlled, side reactions can be
easily prevented.
[0189] A general method of living anionic polymerization using the
microreactor will be described with reference to FIG. 1 showing a
schematic diagram of the microreactor.
[0190] A first monomer and a polymerization initiator for
initiating polymerization are introduced from tube reactors P1 and
P2 (7 and 8 in FIG. 1) into a T-shaped micromixer M1 (1 in FIG. 1)
including a flow passage in which a plurality of liquids can be
mixed, and the first monomer is subjected to living anionic
polymerization in the T-shaped micromixer M1 to thereby form a
first polymer (step 1).
[0191] Next, the first polymer obtained is transferred to a
T-shaped micromixer M2 (2 in FIG. 1). In the micromixer M2, a
reaction control agent introduced from a tube reactor P3 (9 in FIG.
1) is caused to react with the growing end of the obtained polymer
to thereby control the reaction (step 2).
[0192] In this case, the value of n in general formula (3) can be
controlled by the type and amount used of the reaction control
agent.
[0193] Next, the first polymer subjected to reaction control in the
T-shaped micromixer M2 is transferred to a T-shaped micromixer M3
(3 in FIG. 1), and a second monomer introduced from a tube reactor
P4 and the first polymer subjected to reaction control are
subjected to living anionic polymerization continuously in the
mixer M3 (step 3).
[0194] Then the reaction is quenched with an active
proton-containing compound such as methanol, and a block copolymer
is thereby produced.
[0195] When the polymer (A) represented by general formula (3) is
produced using the microreactor described above, a monomer having
an aromatic ring or a heterocycle is used as the first monomer, and
an organic lithium initiator is used as the initiator to initiate
the reaction, whereby a polymer block of the monomer having an
aromatic ring or a heterocycle, i.e., A.sup.2 described above, (an
organic group, i.e., the organic lithium initiator residue A.sup.1,
is bonded to one end of the polymer block A.sup.2) is obtained.
[0196] Next, the reaction control agent is used to control the
reactivity of the growing end. Then a monomer containing a
(meth)acrylate having a protecting group that can be reconverted
into the anionic group is used as the second monomer and allowed to
react to thereby obtain a polymer block.
[0197] Then a deprotection reaction such as hydrolysis is performed
to reconvert the protecting groups into the anionic groups, and
A.sup.3 described above, i.e., a polymer block having the anionic
groups, is thereby obtained.
[0198] A detailed description will be given of the method for
reconverting an ester bond in the protecting group that can be
reconverted into the anionic group into the anionic group by a
deprotection reaction such as hydrolysis.
[0199] The hydrolysis reaction of the ester bond proceeds under
acidic conditions and also under basic conditions, but the
conditions vary slightly depending on the type of ester
bond-containing group. For example, when the ester bond-containing
group is a primary alkoxycarbonyl group such as a methoxycarbonyl
group or a secondary alkoxycarbonyl group such as an
isopropoxycarbonyl group, a carboxyl group can be obtained by
hydrolysis under basic conditions. Examples of a basic compound
used to form the basic conditions in this case include metal
hydroxides such as sodium hydroxide and potassium hydroxide.
[0200] When the ester bond-containing group is a tertiary
alkoxycarbonyl group such as a t-butoxycarbonyl group, a carboxyl
group can be obtained by hydrolysis under acidic conditions.
Examples of an acidic compound used to form the acidic conditions
in this case include: mineral acids such as hydrochloric acid,
sulfuric acid, and phosphoric acid; Bronsted acids such as
trifluoroacetic acid; and Lewis acids such as trimethylsilyl
triflate. The reaction conditions of hydrolysis of a
t-butoxycarbonyl group under acidic conditions are disclosed in,
for example, "Yukikagoubutsu-no-gosei-IV (Synthesis of Organic
Compounds IV), Nihon-kagakukai-hen-dai-5-han Jikken-kagaku-kouza-16
(the Fifth Series of Experimental Chemistry Vol. 16, Ed. by the
Chemical Society of Japan)."
[0201] Another example of the method for converting the
t-butoxycarbonyl group into a carboxyl group is a method in which a
cation exchange resin is used instead of the acid described above.
Examples of the cation exchange resin include resins having, in
their polymer side chains, acid groups such as carboxyl groups
(--COOH) and sulfo groups (--SO.sub.3H). Of these, a strongly
acidic cation exchange resin having sulfo groups in its side chains
is preferable because the rate of the reaction can be increased.
Examples of the commercial product of the cation exchange resin
that can be used in the present invention include strongly acidic
cation exchange resin "Amberlite" manufactured by Organo
Corporation. The amount of the cation exchange resin used is
preferably within the range of 5 to 200 parts by mass and more
preferably within the range of 10 to 100 parts by mass based on 100
parts by mass of the polymer represented by general formula (3)
above because hydrolysis can be performed effectively.
[0202] When the ester bond-containing group is a
phenylalkoxycarbonyl group such as a benzyloxycarbonyl group, the
phenylalkoxycarbonyl group can be converted into a carboxyl group
through a hydrogenation reduction reaction. In this case, the
phenylalkoxycarbonyl group can be reconverted into a carboxyl group
quantitatively by performing the reaction using hydrogen gas as a
reducing agent in the presence of a palladium catalyst such as
palladium acetate under the reaction condition of room
temperature.
[0203] As described above, the reaction conditions for conversion
into a carboxyl group vary depending on the type of ester
bond-containing group. For example, a polymer obtained by
copolymerization using t-butyl (meth)acrylate and n-butyl
(meth)acrylate as raw materials of A.sup.3 has t-butoxycarbonyl
groups and n-butoxycarbonyl groups. Under the acidic conditions
under which the t-butoxycarbonyl groups are hydrolyzed, the
n-butoxycarbonyl groups are not hydrolyzed, so that only the
t-butoxycarbonyl groups can be selectively hydrolyzed and converted
into carboxyl groups through deprotection. Therefore, the acid
value of the hydrophilic block (A.sup.3) can be controlled by
selecting, as raw material monomers of A.sup.3, appropriate
monomers each containing a (meth)acrylate having a protecting group
that can be reconverted into an anionic group.
[0204] It is advantageous in terms of the stability of an aqueous
pigment dispersion to be obtained that, in the polymer (A)
represented by general formula (3) above, the polymer block
(A.sup.2) and the polymer block (A.sup.3) are distinctly separated
from each other. The molar ratio of the polymer block (A.sup.2) to
the polymer block (A.sup.3), A.sup.2:A.sup.3, is preferably within
the range of 100:10 to 100:500. If the ratio of A.sup.3 to A.sup.2
is less than 10/100, the dispersion stability of the pigment and
the ejection stability during inkjet ejection tend to deteriorate.
If the ratio of A.sup.3 to A.sup.2 exceeds 500/100, the
hydrophilicity of the polymer becomes excessively high. In this
case, when paper, for example, is used as a recording medium, the
ink easily permeates the recording medium, and this causes
deterioration in color development. In particular, the ratio
A.sup.2:A.sup.3 is preferably 100:10 to 100:450.
[0205] In the polymer (A) represented by general formula (3) above,
the number of units of the monomer having an aromatic ring or a
heterocycle and forming the polymer block (A.sup.2) is preferably
within the range of 5 to 40, more preferably within the range of 6
to 30, and most preferably within the range of 7 to 25. The number
of anionic groups included in the polymer block (A.sup.3) is
preferably within the range of 3 to 20, more preferably within the
range of 4 to 17, and most preferably within the range of 5 to
15.
[0206] When the molar ratio of the polymer block (A.sup.2) to the
polymer block (A.sup.3), A.sup.2:A.sup.3, is represented by the
molar ratio of the number of moles of the aromatic rings or
heterocycles included in the polymer block (A.sup.2) to the number
of moles of the anionic groups included in (A.sup.3), this ratio is
preferably 100:7.5 to 100:400.
[0207] The acid value of the polymer (A) represented by general
formula (3) above is preferably 40 to 400 mg KOH/g, more preferably
40 to 300 mg KOH/g, and most preferably 40 to 190 mg KOH/g. If the
acid value is less than 40 mg KOH/g, the dispersion stability of
the pigment and the ejection stability during inkjet ejection may
be insufficient. If the acid value exceeds 400 mg KOH/g, the
hydrophilicity of the polymer increases, and the ink easily
permeates a recording medium, so that color development
deteriorates. When the acid value exceeds 190 mg KOH/g, the water
resistance of the ink obtained is affected in some cases.
[0208] The acid value of the polymer in the present invention is an
acid value obtained by the same acid value measurement method as
that for the fine particles of the polymer (A).
(Neutralizer: Basic Compound)
[0209] Preferably, the anionic groups in the polymer (A) are
neutralized.
[0210] Any well-known and commonly used basic compound can be used
for the basic compound for neutralizing the anionic groups in the
polymer (A). For example, inorganic basic materials such as alkali
metal hydroxides, e.g., sodium hydroxide and potassium hydroxide,
and organic basic compounds such as ammonia, triethylamine, and
alkanolamines can be used.
[0211] In the present invention, it is not necessary that the
degree of neutralization of the polymer (A) present in the aqueous
pigment dispersion be 100% with respect to the acid value of the
polymer. Specifically, the anionic groups are neutralized such that
the degree of neutralization of the polymer (A) is preferably 20%
to 200% and more preferably 80% to 150%.
[0212] In the present invention, no particular limitation is
imposed on the method for producing the aqueous inks for inkjet
recording, and any known method can be used.
[0213] For example, one method that can be used includes: mixing
the pigment, the pigment dispersant, water, the binder resin, and
optional various additives under stirring; dispersing and milling
them using any of various dispersing devices and ink mills such as
a bead mill, an ultrasonic homogenizer, a high-pressure
homogenizer, a paint shaker, a ball mill, a roll mill, a sand mill,
a sand grinder, a DYNO-MILL, a Dispermat, an SC-MILL, and a
Nanomizer; adding and mixing the rest of the materials; and
adjusting the viscosity appropriately.
[0214] Each of the aqueous inks can also be prepared by: adding a
water-soluble solvent and/or water, the binder resin, and optional
various additives to a self-dispersible pigment or a
high-concentration dispersion (mill base) prepared in advance by
using any of the above-described dispersing devices; mixing and
stirring the resulting mixture; and diluting the mixture to the
desired viscosity. By changing the pigment and the pigment
concentration, aqueous color inks mutually different in at least
one of hue, lightness, and chroma can be prepared. It is preferable
to use a high-concentration dispersion prepared by dispersing the
pigment with the aid of the polymer (A).
(Additional Additives)
[0215] The aqueous inks for inkjet recording according to the
present invention can also be produced by adding a water-soluble
solvent and/or water, the binder resin, etc. and optionally adding
a humectant (drying inhibitor), a penetrant, and other additives
according to the desired physical properties.
[0216] After the preparation of each ink, a centrifugal step or a
filtration step may be additionally performed.
(Humectant)
[0217] The humectant is added for the purpose of preventing drying
of the ink. The humectant added for the purpose of preventing
drying is contained in the ink in an amount of preferably 3 to 50%
by mass.
[0218] No particular limitation is imposed on the humectant used in
the present invention. It is preferable that the humectant is
miscible with water and provides the effect of preventing clogging
of a head of an inkjet printer. Examples of the humectant include
ethylene glycol, diethylene glycol, triethylene glycol,
polyethylene glycol having a molecular weight of 2,000 or less,
dipropylene glycol, tripropylene glycol, 1,3-propylene glycol,
isopropylene glycol, isobutylene glycol, 1,4-butanediol,
1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, meso-erythritol,
and pentaerythritol. In particular, when 1,3-butyl glycol is
contained, excellent effects on ink drying properties and
ejectability are obtained while safety is achieved.
(Penetrant)
[0219] The penetrant is added for the purpose of improving the
penetrability into a recording medium and controlling the diameter
of dots on the recording medium.
[0220] Examples of the penetrant include: lower alcohols such as
ethanol and isopropyl alcohol; ethylene oxide adducts of alkyl
alcohols such as ethylene glycol hexyl ether and diethylene glycol
butyl ether; and propylene oxide adducts of alkyl alcohols such as
propylene glycol propyl ether. The amount of the penetrant
contained in the ink is preferably 0.01 to 10% by mass.
[0221] The amount of the pigment in each of the inks for inkjet
recording is preferably 1 to 20% by mass, in order to obtain a
sufficient image density and to maintain the dispersion stability
of the pigment in the ink.
[0222] If necessary, a preservative, a viscosity modifier, a pH
modifier, a chelating agent, a plasticizer, an antioxidant, an
ultraviolet absorber, etc. may be added.
[0223] The aqueous ink set for inkjet recording according to the
present invention includes the above-described first to n-th
aqueous inks. n is two or more, preferably 2 to 20, and more
preferably 2 to 10.
(Recording Medium)
[0224] No particular limitation is imposed on the recording medium
for the aqueous inks for inkjet recording, and the recording medium
can be an absorptive recording medium, a recording medium having an
ink absorbing layer, a non-absorptive recording medium having no
ink absorbency, a low-absorptive recording medium having low ink
absorbency, etc. One feature of the aqueous inks for inkjet
recording according to the present invention is that good color
development is achieved particularly when recording is performed on
a non-absorptive recording medium or a low-absorptive recording
medium.
[0225] Examples of the absorptive recording medium include copying
paper generally used in copiers (PPC paper), plain paper, fabric,
corrugated cardboards, and wood. Examples of the recording medium
having an absorbing layer include inkjet paper. Specific examples
of the inkjet paper include PICTORICOPRO Photopaper manufactured by
Pictorico. Such an absorptive recording medium prepared by forming
an ink absorbing layer on its surface may be high cost.
[0226] However, non-absorptive recording mediums and low-absorptive
recording mediums are excellent in water resistance and
rub-fastness and advantageous because of their lower cost as
compared with absorptive recording mediums prepared by forming an
ink absorbing layer on their surface. On the other hand, as the
absorbency of the non-absorptive recording mediums and the
low-absorptive recording mediums decreases or when they are
non-absorptive, bleeding is more likely to occur, and it is
difficult to achieve the occurrence of bleeding and recording speed
simultaneously. It is advantageous to use the recording method in
the present invention for these non-absorptive recording mediums
and low-absorptive recording mediums, and it is more advantageous
to use the recording method for the non-absorptive recording
mediums.
[0227] The "low-absorptive recording mediums" and the
"non-absorptive recording mediums" are recording mediums in which
the amount of water absorption from the start of contact until a
lapse of 30 msec. is 10 mL/m.sup.2 or less as measured by the
Bristow method. The Bristow method is the most popular method for
measuring the amount of liquid absorption in a short time and used
in Japan Technical Association of the Pulp and Paper Industry
(JAPAN TAPPI). The details of the test method are described in
Standard No. 51 "Method for testing liquid absorbency of paper and
paper board: Bristow method" in "the 2000 edition of JAPAN TAPPI
paper and pulp testing methods."
[0228] The non-absorptive recording mediums and the low-absorptive
recording mediums can also be classified according to water
wettability of their recording surface. For example, 0.5 .mu.L of a
water droplet is dropped onto the recording surface of a recording
medium, and the rate of reduction in contact angle is measured
(this can be obtained by comparing the contact angle at 0.5 msec.
after landing of the droplet with the contact angle at 5 seconds
after the landing). This rate of reduction in contact angle can be
used to characterize the recording medium. More specifically, as
for properties of recording mediums, the non-absorptive in a
"non-absorptive recording medium" means that the above rate of
reduction is less than 1%, and the low-absorptive in a
"low-absorptive recording medium" means that the above rate of
reduction is 1% or more and less than 5%. Absorptive means that the
above rate of reduction is 5% or more. The contact angle can be
measured using, for example, a portable contact angle meter PCA-1
(manufactured by Kyowa Interface Science Co., Ltd.).
[0229] Examples of the non-absorptive recording medium include
plastic films, recording mediums prepared by coating substrates
such as paper substrates with plastics, and recording mediums
prepared by bonding plastic films to these substrates. For example,
products used as food packaging materials can be used, and
well-known plastic films can be used. Specific examples include:
polyester films such as polyethylene terephthalate films and
polyethylene naphthalate films; polyolefin films such as
polyethylene films and polypropylene films; polyamide-based films
such as nylon films; polystyrene films; polyvinyl alcohol films;
polyvinyl chloride films; polycarbonate films; polyacrylonitrile
films; and polylactic acid films. In particular, polyester films,
polyolefin films, and polyamide-based films are preferred, and
polyethylene terephthalate, polypropylene, and nylon are more
preferred. The above films may be coated with, for example,
polyvinylidene chloride in order to impart barrier properties. A
film on which a vapor deposition layer of a metal such as gold,
silver, copper, or aluminum or a metal oxide such as silica or
alumina has been deposited may also be used as needed.
[0230] The above plastic films may be unstretched films or may be
uniaxially or biaxially stretched films. The surface of each film
may be untreated. However, it is preferable that the film is
subjected to treatment such as corona discharge treatment, ozone
treatment, low-temperature plasma treatment, flame treatment, glow
discharge treatment, etc. in order to improve its adhesion.
[0231] The thickness of the plastic film is appropriately changed
according to its intended application. For example, when the film
is used for a soft packaging application, the thickness of the film
is preferably 10 .mu.m to 100 .mu.m so that the film can have
flexibility, durability, and curling resistance. The thickness is
more preferably 10 .mu.m to 30 .mu.m. Specific examples of such a
film include PYLEN (registered trademark) available from TOYOBO
Co., Ltd.
[0232] No particular limitation is imposed on the low-absorptive
recording mediums, and examples thereof include coated paper
prepared by forming a coating layer for absorbing oil-based inks on
the surface of high-quality or acid-free paper that is formed
mainly of cellulose and is generally not surface-treated. Specific
examples include paper surface-coated with a coating to improve its
appearance and smoothness and classified as coated paper for
printing in "PRODUCTION STATISTICS CLASSIFICATION" by the Ministry
of Economy, Trade and Industry. Examples of the coating include a
coating prepared by mixing a white inorganic compound pigment such
as clay (kaolin) or calcium carbonate and an adhesive (binder) such
as starch. The coating amount of the coating is preferably about 10
to about 40 g/m.sup.2. No particular limitation is imposed on the
coated paper, and art paper such as printing paper, enamel paper,
light coated paper, lightweight coated paper, etc. can be used.
Examples of the low-absorptive recording mediums include:
lightweight coated paper such as "OK EVERLIGHT COAT" manufactured
by Oji Paper Co., Ltd. and "AURORA S" manufactured by Nippon Paper
Industries Co., Ltd.; light coated paper (A3) such as "OK Coat L"
manufactured by Oji Paper Co., Ltd. and "AURORA L" manufactured by
Nippon Paper Industries Co., Ltd.; enamel paper (A2, B2) such as
"OK Top Coat+" manufactured by Oji Paper Co., Ltd. and "AURORA
Coat" manufactured by Nippon Paper Industries Co., Ltd.; and art
paper (A1) such as "OK KINFUJI+" manufactured by Oji Paper Co.,
Ltd. and "Tokubishi Art" manufactured by Mitsubishi Paper Mills
Limited.
EXAMPLES
[0233] The present invention will next be described in more detail
by way of Examples.
(Method for preparing polymer (A))
Synthesis Example 1
[0234] Butyllithium (BuLi) used as the polymerization initiator and
styrene (St) used as the first monomer were introduced from the
tube reactors P1 and P2 in FIG. 1 into the T-shaped micromixer M1
in FIG. 1 and subjected to living anionic polymerization to form a
polymer.
[0235] Next, the polymer obtained was transferred to the T-shaped
micromixer M2 in FIG. 1 through the tube reactor R1 in FIG. 1, and
a reaction control agent (.alpha.-methylstyrene (.alpha.-MeSt))
introduced from the tube reactor P3 in FIG. 1 was caused to react
with the growing end of the polymer.
[0236] Next, tert-butyl methacrylate (t-BMA) used as the second
monomer was introduced into the T-shaped micromixer M3 from the
tube reactor P4 in FIG. 1. The second monomer and the polymer
transferred through the tube reactor R2 in FIG. 1 were subjected to
a continuous living anionic polymerization reaction. Then the
reaction was quenched with methanol to thereby produce a block
copolymer (PA-1).
[0237] In this process, the entire microreactor was immersed in a
thermostatic bath to set the reaction temperature to 24.degree. C.
Each of the monomers and the reaction control agent introduced into
the microreactor was dissolved in tetrahydrofuran (THF). The BuLi
used was a commercial 2.6M hexane solution, and this solution was
diluted with hexane. The amounts of the monomers forming the block
copolymer (PA-1) were controlled by the concentration and
introduction rate of the diluted solution (Table 1).
[0238] The block copolymer (PA-1) obtained was treated with a
cation exchange resin to hydrolyze the copolymer. The reaction
solution was subjected to evaporation under reduced pressure, and
the solids obtained were pulverized to obtain polymer (P-1)
(powder).
(Methods for Measuring Physical Properties of Polymer)
[0239] The physical properties of the polymer (P-i) obtained were
measured as follows.
(Method for Measuring Number Average Molecular Weight (Mn) and
Weight Average Molecular Weight (Mw))
[0240] The measurement was performed by gel permeation
chromatography (GPC) under the following conditions.
[0241] Measurement device: High performance GPC ("HLC-8220GPC"
manufactured by TOSOH Corporation)
[0242] Columns: The following columns manufactured by TOSOH
Corporation were connected in series and used.
[0243] "TSKgel G5000" (7.8 mm I.D..times.30 cm).times.1
[0244] "TSKgel G4000" (7.8 mm I.D..times.30 cm).times.1
[0245] "TSKgel G3000" (7.8 mm I.D..times.30 cm).times.1
[0246] "TSKgel G2000" (7.8 mm I.D..times.30 cm).times.1
[0247] Detector: RI (refractive index detector)
[0248] Column temperature: 40.degree. C.
[0249] Eluent: tetrahydrofuran (THF)
[0250] Flow rate: 1.0 mL/min
[0251] Injection amount: 100 .mu.L (THF solution with a sample
concentration of 0.4% by mass)
[0252] Standard samples: The following polystyrene standards were
used to produce a calibration curve.
(Polystyrene Standards)
[0253] "TSKgel standard polystyrene A-500" manufactured by TOSOH
Corporation
[0254] "TSKgel standard polystyrene A-1000" manufactured by TOSOH
Corporation
[0255] "TSKgel standard polystyrene A-2500" manufactured by TOSOH
Corporation
[0256] "TSKgel standard polystyrene A-5000" manufactured by TOSOH
Corporation
[0257] "TSKgel standard polystyrene F-1" manufactured by TOSOH
Corporation
[0258] "TSKgel standard polystyrene F-2" manufactured by TOSOH
Corporation
[0259] "TSKgel standard polystyrene F-4" manufactured by TOSOH
Corporation
[0260] "TSKgel standard polystyrene F-10" manufactured by TOSOH
Corporation
[0261] "TSKgel standard polystyrene F-20" manufactured by TOSOH
Corporation
[0262] "TSKgel standard polystyrene F-40" manufactured by TOSOH
Corporation
[0263] "TSKgel standard polystyrene F-80" manufactured by TOSOH
Corporation
[0264] "TSKgel standard polystyrene F-128" manufactured by TOSOH
Corporation
[0265] "TSKgel standard polystyrene F-288" manufactured by TOSOH
Corporation
[0266] "TSKgel standard polystyrene F-550" manufactured by TOSOH
Corporation
(Method for Measuring Acid Value)
[0267] The measurement was performed according to JIS test method K
0070-1992. Specifically, 0.5 g of the polymer was dissolved in a
tetrahydrofuran (THF) solvent, and titration with a 0.1M alcohol
solution of potassium hydroxide was performed using phenolphthalein
as an indicator to determine the acid value.
(Method for Measuring Solubility in Water)
[0268] Sieves with mesh sizes of 250 .mu.m and 90 .mu.m were used
to screen the polymer such that its particle diameter fell within
the range of 250 .mu.m to 90 .mu.m. 0.5 g of the resulting polymer
was sealed in a bag formed from a 400-mesh wire net, immersed in 50
mL of water, and left under mild stirring at a temperature of
25.degree. C. for 24 hours. After immersion for 24 hours, the
400-mesh wire net with the polymer sealed therein was dried in a
dryer set at 110.degree. C. for 2 hours to dry the polymer. The
change in weight of the 400-mesh wire net with the polymer sealed
therein before and after the immersion in water was measured, and
the solubility was computed using the following expression.
Solubility (g/100 mL)=(Polymer-sealed 400-mesh wire net before
immersion (g)-Polymer-sealed 400-mesh wire net after immersion
(g)).times.2 [Math. 7]
(Method for Determining Formation of Fine Particles in Water and
method for measuring average particle diameter (nm))
[0269] (1) The acid value of the polymer was determined according
to the above-described method for measuring the acid value.
[0270] (2) 1 g of the polymer was added to 50 mL of water, and a
0.1 mol/L aqueous potassium hydroxide solution was added in an
amount sufficient to completely neutralize the polymer having the
acid value obtained in (1) above to thereby completely neutralize
the polymer.
[0271] (3) The completely neutralized solution was subjected to
ultrasonic waves at a temperature of 25.degree. C. for 2 hours
using an ultrasonic cleaner (ultrasonic cleaner US-102, SND Co.,
Ltd., 38 kHz, self-excited oscillation) to disperse the polymer and
was then left to stand at room temperature for 24 hours.
[0272] After the solution was left to stand for 24 hours, a sample
solution was sampled at a depth of 2 cm from the surface of the
solution. Then a dynamic light scattering particle size measurement
device "Microtrac particle size distribution analyzer UPA-ST150"
manufactured by NIKKISO Co., Ltd. was used to determine whether or
not information about light scattering due to the formation of fine
particles was obtained, whereby the presence of fine particles was
checked. During the measurement, the average particle diameter was
also measured.
(Method for Measuring Surface Tension)
[0273] The same sample solution as that obtained in the method for
determining the formation of fine particles in water was used, and
a value measured using a Wilhelmy surface tension meter CBVP-Z
(manufactured by Kyowa Interface Science Co., Ltd.) was used as the
surface tension.
[0274] In the measurement, the temperature of the measurement
sample was adjusted to 25.degree. C., and 10 g of the ink was
filled into a petri dish with a diameter of 40 mm. A glass plate
with a hook manufactured by Kyowa Interface Science Co., Ltd.
(specification values: thickness 0.3 mm, width 23.9 mm, peripheral
length 95.6 mm, weight 0.54 g) was used as a probe.
TABLE-US-00001 TABLE 1 Synthesis Example 1 Polymer (A) P-14
Reaction temperature 24.degree. C. Initiator Type BuLi Moles 1.0
First monomer Type St Moles 12.0 Reaction control agent Type
.alpha.-MeSt Moles 2.0 Second monomer Type tBMA Moles 8.1 Molar
ratio of polymer block (A.sup.2) formed A.sup.2:A.sup.3 = 100:76
from first monomer to polymer block (A.sup.3) formed from second
monomer Number average molecular weight 2471 Acid value mg KOH/g
148 Solubility in water 0.0056 (g/100 mL) Presence of fine
particles when degree of neutralization of Yes/48 anionic groups is
100%/volume average particle diameter (nm) Surface tension (mN/m)
67.7
[0275] In Tables 1 and 2, BuLi stands for normal butyllithium, St
stands for styrene, DPE stands for 1,1-diphenylethylene,
.alpha.MeSt stands for .alpha.-methylstyrene, and tBMA stands for
tert-butyl methacrylate.
(Production Examples: Methods for Producing Aqueous Pigment
Dispersions)
[0276] Aqueous pigment dispersions were obtained using the
following methods in Production Examples. The amounts of raw
materials used are shown in tables shown later.
Production Example 1
Method for Producing Aqueous Pigment Dispersion (C-i)
[0277] Step 1 was performed. Specifically, a 1.0 L intensive mixer
(Nippon Eirich Co., Ltd.) was charged with 150 parts by mass of a
phthalocyanine-based pigment FASTOGEN Blue Pigment (C.I. Pigment
15:3, manufactured by DIC Corporation) used as the pigment, 30
parts by mass of the polymer (P-1) used as the polymer (A), 150
parts by mass of triethylene glycol used as a water-soluble organic
solvent, and 20 parts by mass of a 34% aqueous potassium hydroxide
solution, and then the mixture was kneaded at a rotor peripheral
speed of 2.94 m/s and a jacket peripheral speed of 1 m/s for 25
minutes.
[0278] Next, step 2 was performed. Specifically, 450 parts by mass
of ion exchanged water was gradually added to the kneaded mixture
in the container of the intensive mixer under continuous stirring,
and then 185 parts by mass of ion exchanged water was added and
mixed. An aqueous pigment dispersion (C-1) with a pigment
concentration of 15.0% was thereby obtained.
Production Example 2
Method for Producing Aqueous Pigment Dispersion (Y-1)
[0279] An aqueous pigment dispersion in Production Example 2 was
obtained in the same manner as in Production Example 1 except that
the type of the pigment was changed.
[0280] The compositions in Production Examples 1 and 2 are shown in
Table 2.
TABLE-US-00002 TABLE 2 Production Production Example 1 Example 2
Name of aqueous pigment dispersion C-1 Y-1 Type of pigment PB15:3
PY74 Amount of pigment (parts by mass) 150 150 Type of polymer (A)
P-1 P-1 Amount of polymer (A) (parts by mass) 30 30 Acid value of
polymer (A) 148 148 Mass ratio of polymer (A)/pigment 0.2 0.2 Step
1 Type of water-soluble solvent TEG TEG Amount of water-soluble
solvent 150 150 (parts by mass) Amount of KOH (parts by mass) 20 20
Step 2 Dispersion medium: first addition Water = 450 Water = 450
(parts by mass) Dispersion mediums: second TEG: water = TEG: water
= addition (parts by mass) 0/185 0/185 Volume average particle
diameter (nm) 101.2 94.1 of aqueous pigment dispersion Number of
coarse particles with volume 1 3 average particle diameter of 1.0
.mu.m or more (.times.10.sup.6/mL)
[0281] The abbreviations in the table are as follows. PB15:3:
Phthalocyanine-based pigment FASTOGEN Blue Pigment (C.I. Pigment
15:3 manufactured by DIC Corporation)
[0282] PY74: Pigment Yellow 74
[0283] KOH: 34% Aqueous potassium hydroxide solution
[0284] TEG: Triethylene glycol
[0285] Water: Ion exchanged water
(Method for Preparing Binder Resin)
Synthesis Example 2
[0286] A four-neck flask equipped with a stirrer, a thermometer, a
cooling tube, and a nitrogen introduction tube was charged with 16
parts by mass of "Newcol 707SF" [an anionic emulsifier manufactured
by Nippon Nyukazai Co., Ltd.], 6.5 parts by mass of "NOIGEN
TDS-200D" [a nonionic emulsifier manufactured by DAI-ICHI KOGYO
SEIYAKU Co., Ltd.], and 220 parts by mass of deionized water. The
temperature of the mixture was increased to 80.degree. C. under
nitrogen flow, and then an aqueous solution prepared by dissolving
0.8 parts by mass of ammonium persulfate in 16 parts by mass of
deionized water was added. Then a mixture of 60 parts by mass of
2-ethylhexyl acrylate, 100 parts by mass of styrene, 27 parts by
mass of methyl methacrylate, 0.4 g of
3-methacryloxypropyltrimethoxysilane, 3 parts by mass of
acrylamide, and 6 parts by mass of methacrylic acid was added
dropwise over 3 hours. After completion of the dropwise addition,
the resulting mixture was allowed to react for 2 hours, cooled to
25.degree. C., and neutralized with 1.5 parts by mass of 28 mass%
ammonia water, and deionized water was added to adjust the amount
of non-volatile components to 45% by mass, whereby an aqueous
acrylic resin dispersion (X-1) having a glass transition
temperature (T parts) of 35.degree. C. and an average particle
diameter of 60 nm was obtained. The final solid content of the
acrylic resin dispersion (X-1) was 39%.
(Preparation of Additive Composition V)
[0287] 8.0 Parts by mass of propylene glycol, 6.0 parts by mass of
3-methoxybutanol, 7.0 parts by mass of glycerin, 0.7 parts by mass
of triethylene glycol, 2.0 parts by mass of SC-P1000, 5.0 parts by
mass of ethylene urea, 0.012 parts by mass of TEGO WET KL245, 0.2
parts of triethanolamine, and 0.1 parts by mass ACTICIDE B20 were
added to prepare additive composition V.
(Preparation of Aqueous Inks for Inkjet Recording)
[0288] 33.3% by mass of the aqueous pigment dispersion obtained in
Production Example 1 or 2 (the concentration of the pigment in the
ink was 5% by mass), 17.8% by mass of the aqueous acrylic resin
dispersion (X-1) obtained in Synthesis Example 3 (the acrylic resin
in the ink was 7% by mass), 29.0% by mass of the additive
composition V, and 0.4% by mass of one of surfactants shown in
Tables 4 to 6 were added, and pure water was used to adjust the
total amount to 100 parts by mass, whereby an aqueous ink for
inkjet recording was obtained.
TABLE-US-00003 TABLE 3 Manufacturer name Product name Skeleton HLB
A Air Products and Chemicals, Inc. SURFYNOL 440 Acetylene-based 8 B
Air Products and Chemicals, Inc. SURFYNOL MD-20 Acetylene-based 3 C
Air Products and Chemicals, Inc. SURFYNOL DF-110D Acetylene-based 3
D EVONIK TEGO Wet KL245 Silicone-based ND E EVONIK TEGO Wet 270
Silicone-based ND F Nissin Chemical Co., Ltd. SILFACE SAG014
Silicone-based 9 G Air Products and Chemicals, Inc. SURFYNOL104PG50
Acetylene-based 4 H Air Products and Chemicals, Inc. SURFYNOL 420
Acetylene-based 4 I Air Products and Chemicals, Inc. EnviroGem AD01
Acetylene-based 4 J Air Products and Chemicals, Inc. SURFYNOL SEF
Acetylene-based 6
TABLE-US-00004 TABLE 4 1-A 1-B 1-C 1-D 1-E 1-F 1-G 1-H 1-I 1-J
Aqueous pigment C-1 C-1 C-1 C-1 C-1 C-1 C-1 C-1 C-1 C-1 dispersion
Mass % of aqueous 33.3 33.3 33.3 33.3 33.3 33.3 33.3 33.3 33.3 33.3
pigment dispersion Mass % of aqueous 17.8 17.8 17.8 17.8 17.8 17.8
17.8 17.8 17.8 17.8 acrylic resin dispersion (X-1) Mass % of
additive 29.0 29.0 29.0 29.0 29.0 29.0 29.0 29.0 29.0 29.0
composition V Surfactant A B C D E F G H I J Mass % of surfactant
0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Mass % of water Balance
Balance Balance Balance Balance Balance Balance Balance Balance
Balance Aqueous ink 100 100 100 100 100 100 100 100 100 100 (Total
mass %) Surface tension 34.2 32.2 30.3 32.5 29.9 32.8 32.7 33.4
34.4 32.7 (mN/m) of aqueous ink
TABLE-US-00005 TABLE 5 2-A 2-B 2-C 2-D 2-E 2-F 2-G 2-H 2-I 2-J
Aqueous pigment Y-1 Y-1 Y-1 Y-1 Y-1 Y-1 Y-1 Y-1 Y-1 Y-1 dispersion
Mass % of aqueous 33.3 33.3 33.3 33.3 33.3 33.3 33.3 33.3 33.3 33.3
pigment dispersion Mass % of aqueous 17.8 17.8 17.8 17.8 17.8 17.8
17.8 17.8 17.8 17.8 acrylic resin dispersion (X-1) Mass % of
additive 29.0 29.0 29.0 29.0 29.0 29.0 29.0 29.0 29.0 29.0
composition V Surfactant A B C D E F G H I J Mass % of surfactant
0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Mass % of water Balance
Balance Balance Balance Balance Balance Balance Balance Balance
Balance Aqueous ink 100 100 100 100 100 100 100 100 100 100 (Total
mass %) Surface tension 34.4 32.4 30.4 32.7 30.5 32.8 32.9 33.6
34.6 32.9 (mN/m)of aqueous ink
Production Example 4
Method for Producing Aqueous Inks for Inkjet Recording
[0289] Aqueous inks for inkjet recording were prepared by using
additive compositions V with different composition ratios and a
surfactant named "A" in Table 3.
[0290] The compositions are shown in Table 6.
TABLE-US-00006 TABLE 6 3-A 4-A 5-A 6-A Aqueous pigment dispersion
C-1 Y-1 Y-1 Y-1 Mass % of PG 14.0 14.0 8.0 8.0 Mass % of MB 0.0 0.0
13.0 13.0 Mass % of GLYB 7.0 7.0 0.0 5.0 Mass % of TEGB 6.0 6.0 6.0
6.0 Mass % of SC-P1000B 2.0 2.0 2.0 2.0 Mass % of ethylene urea 5.0
5.0 5.0 0.0 Mass % of KL245 0.012 0.012 0.012 0.012 Mass % of
triethanolamine 0.2 0.2 0.2 0.2 Mass % of ACTICIDE B20 0.1 0.1 0.1
0.1 Mass % of Polymer A 7 7 7 7 Mass % of surfactant A A A A Mass %
of surfactant 0.4 0.4 0.4 0.4 Mass % of water Balance Balance
Balance Balance Aqueous ink 100 100 100 100 (Total mass %) Surface
tension (mN/m) of 35.2 35.5 34.2 35.8 aqueous ink
[0291] The abbreviations in the table are as follows.
[0292] PG: Propylene glycol manufactured by Wako Pure Chemical
Industries, Ltd.
[0293] MB: 3-Methoxy-1-butanol manufactured by Daicel
Corporation
[0294] GLY: Refined glycerin manufactured by Kao Corporation
[0295] TEG: Triethylene glycol manufactured by NIPPON SHOKUBAI Co.,
Ltd.
[0296] SC-P1000: Polyoxypropylene(14) polyglyceryl ether
manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.
[0297] Ethylene urea: 2-Imidazolidinone manufactured by TOKYO
CHEMICAL INDUSTRY Co., Ltd.
[0298] KL245: Silicone-based surfactant TEGOWET KL245 manufactured
by EVONIK
[0299] Triethanolamine: manufactured by Mitsui Chemicals, Inc.
[0300] ACTICIDE B20: manufactured by Thor Japan
(Evaluation of Aqueous Inks)
[0301] The produced aqueous inks for inkjet recording were
evaluated as follows.
[Evaluation of Bleeding of Aqueous Inks for Inkjet Recording]
[0302] Two different color inks selected from among the produced
aqueous inks for inkjet recording were filled into inkjet heads
KJ4B-YH manufactured by KYOCERA Corporation. The hydraulic head
difference between a head nozzle plate surface and ink subtanks was
set to +35 cm, and a negative pressure of -5.0 kPa was used to
adjust a supply pressure. The gap between each inkjet head and a
recording medium ("OK Top Coat+" manufactured by Oji Paper Co.,
Ltd.) was set to 1.2 mm. The heads were driven under the following
conditions. The standard voltage of the inkjet heads and their
standard temperature were used, and the size of droplets was set to
12 pL to perform printing. The distance between the inkjet heads
was 6 cm, and a print was produced at a printing speed of 100
m/min, which is the maximum printing speed using the 600 dpi heads
at 600 pi. Under these conditions, the time interval between
landing of droplets of a first ink and landing of droplets of the
next ink is 36 milliseconds. Prints were produced using various
combinations of inks and visually observed under a microscope
(40.times.). Bleeding between two different color aqueous inks for
inkjet recording was evaluated according to the following criteria
(see FIG. 2).
[0303] AA: Color mixing occurred only in a contact portion between
two different color dots.
[0304] A: Color mixing occurred also in portions other than the
contact portion between two different color dots, but the original
colors were still present.
[0305] C: Two different color dots were completely mixed to form a
secondary color.
[Offset Resistance of Inks]
[0306] One of the produced aqueous inks for inkjet recording was
spread over an A2 coated paper sheet "OK Top Coat+" manufactured by
Oji Paper Co., Ltd. applied to a copper plate using a #12 bar
coater, and the resulting paper sheet was placed on a hot plate
heated to 150.degree. C. for 5 seconds to dry the ink. Immediately
after this, the resulting colored paper sheet was transferred to
another hot plate heated to 100.degree. C., and a white coated
paper sheet was placed on the colored paper sheet. A weight was
placed on the white coated paper sheet such that a load of 100
g/cm.sup.2 was applied and was left to stand for 1 minute.
[0307] After a lapse of 1 minute, the weight was removed, and the
white coated paper sheet was peeled off the colored paper sheet.
Then the ratio of the coating remaining on the colored paper sheet
was analyzed using image analysis software "ImageJ" and evaluated
according to the following criteria.
[0308] A: The ratio of the coating remaining on the colored paper
sheet was 80% or more.
[0309] C: The ratio of the coating remaining on the colored paper
sheet was less than 80%.
[Ejection Stability]
[0310] Under the same conditions as those in the [Evaluation of
bleeding of aqueous inks for inkjet recording], an ejection test
was performed to check ejection stability. Specifically, the same
procedure as in the [Evaluation of bleeding of aqueous inks for
inkjet recording] was repeated to perform printing, and the absence
of start-up delay in a printed pattern and the absence of nozzle
missing were checked. Then the heads were left to stand for 30
minutes without head caps. Then a second print was produced without
recovery operation such as ink purging.
[0311] The occurrence of image irregularities in a print start
position of the second print pattern due to start-up delay and the
occurrence of nozzle missing were evaluated according to the
following criteria.
[0312] A: No image irregularities were found in the print start
position, and no nozzle missing occurred.
[0313] C: Image irregularities were found in the print start
position, and blank spots due to nozzle missing were found in some
positions.
[0314] The results are shown in the following tables.
TABLE-US-00007 TABLE 7 Reference Example Example Example Example
Comparative Comparative Ink set Example 1 2 3 4 Example 1 Example 2
First ink 1-A 1-A 1-A 1-A 1-A 1-A 1-A Surface tension of 34.2 34.2
34.2 34.2 34.2 34.2 34.2 first ink (mN/m) Second ink None 2-A 2-B
2-D 2-F 2-C 2-E Surface tension of -- 34.4 32.4 32.7 32.8 30.4 30.5
second ink (mN/m) Difference in surface -- 0.2 -1.8 -1.5 -1.4 -3.8
-3.7 tension between first and second inks (mN/m) Bleeding -- AA AA
AA A C C Offset resistance of ink A A A A A A A Ejection stability
A A A A A A A
TABLE-US-00008 TABLE 8 Reference Example Example Example Example
Example Example Ink set Example 5 6 7 8 9 10 First ink 1-B 1-B 1-B
1-B 1-B 1-B 1-B Surface tension of 32.2 32.2 32.2 32.2 32.2 32.2
32.2 first ink (mN/m) Second ink None 2-A 2-B 2-C 2-D 2-E 2-F
Surface tension of -- 34.4 32.4 30.4 32.7 30.5 32.8 second ink
(mN/m) Difference in surface -- 2.2 0.2 -1.8 0.5 -1.7 0.6 tension
between first and second inks (mN/m) Bleeding -- AA AA A AA AA AA
Offset resistance of ink A A A A A A A Ejection stability A A A A A
A A
TABLE-US-00009 TABLE 9 Reference Example Example Example Example
Example Comparative Ink set Example 11 12 13 14 15 Example 3 First
ink 1-C 1-C 1-C 1-C 1-C 1-C 1-C Surface tension of 30.3 30.3 30.3
30.3 30.3 30.3 30.3 first ink (mN/m) Second ink None 2-B 2-C 2-D
2-E 2-F 2-A Surface tension of -- 32.4 30.4 32.7 30.5 32.8 34.4
second ink (mN/m) Difference in surface -- 2.1 0.1 2.4 0.2 2.5 4.1
tension between first and second inks (mN/m) Bleeding -- A AA A AA
A C Offset resistance of ink A A A A A A A Ejection stability A A A
A A A A
TABLE-US-00010 TABLE 10 Reference Example Example Example Example
Example Example Ink set Example 16 17 18 19 20 21 First ink 1-D 1-D
1-D 1-D 1-D 1-D 1-D Surface tension of 32.5 32.5 32.5 32.5 32.5
32.5 32.5 first ink (mN/m) Second ink None 2-A 2-B 2-C 2-D 2-E 2-F
Surface tension of -- 34.4 32.4 30.4 32.7 30.5 32.8 second ink
(mN/m) Difference in surface -- 1.9 -0.1 -2.1 0.2 -2.0 0.3 tension
between first and second inks (mN/m) Bleeding -- A AA A AA AA AA
Offset resistance of ink A A A A A A A Ejection stability A A A A A
A A
TABLE-US-00011 TABLE 11 Reference Example Example Example Example
Example Comparative Ink set Example 22 23 24 25 26 Example 4 First
ink 1-E 1-E 1-E 1-E 1-E 1-E 1-E Surface tension of 29.9 29.9 29.9
29.9 29.9 29.9 29.9 first ink (mN/m) Second ink None 2-B 2-C 2-D
2-E 2-F 2-A Surface tension of -- 32.4 30.4 32.7 30.5 32.8 34.4
second ink (mN/m) Difference in surface -- 2.5 0.5 2.8 0.6 2.9 4.5
tension between first and second inks (mN/m) Bleeding -- A AA AA AA
A C Offset resistance of ink A A A A A A A Ejection stability A A A
A A A A
TABLE-US-00012 TABLE 12 Reference Example Example Example Example
Example Example Ink set Example 27 28 29 30 31 32 First ink 1-F 1-F
1-F 1-F 1-F 1-F 1-F Surface tension of 32.8 32.8 32.8 32.8 32.8
32.8 32.8 first ink (mN/m) Second ink None 2-A 2-B 2-C 2-D 2-E 2-F
Surface tension of -- 34.4 32.4 30.4 32.7 30.5 32.8 second ink
(mN/m) Difference in surface -- 1.6 -0.4 -2.4 -0.1 -2.3 0.0 tension
between first and second inks (mN/m) Bleeding -- A AA A AA A A
Offset resistance of ink A A A A A A A Ejection stability A A A A A
A A
TABLE-US-00013 TABLE 13 Reference Ink set Example Example 33 First
ink 1-G 1-G Surface tension of first ink 32.7 32.7 (mN/m) Second
ink None 2-G Surface tension of second ink -- 32.9 (mN/m)
Difference in surface tension -- 0.2 between first and second inks
(mN/m) Bleeding -- AA Offset resistance of ink A A Ejection
stability A A
TABLE-US-00014 TABLE 14 Reference Ink set Example Example 34 First
ink 1-H 1-H Surface tension of first ink 33.4 33.4 (mN/m) Second
ink None 2-H Surface tension of second ink -- 33.6 (mN/m)
Difference in surface tension -- 0.2 between first and second inks
(mN/m) Bleeding -- AA Offset resistance of ink A A Ejection
stability A A
TABLE-US-00015 TABLE 15 Reference Ink set Example Example 35 First
ink 1-I 1-I Surface tension of first ink 34.4 34.4 (mN/m) Second
ink None 2-I Surface tension of second ink -- 34.6 (mN/m)
Difference in surface tension -- 0.2 between first and second inks
(mN/m) Bleeding -- AA Offset resistance of ink A A Ejection
stability A A
TABLE-US-00016 TABLE 16 Reference Ink set Example Example 36 First
ink 1-J 1-J Surface tension of first ink 32.7 32.7 (mN/m) Second
ink None 2-J Surface tension of second ink -- 32.9 (mN/m)
Difference in surface tension -- 0.2 between first and second inks
(mN/m) Bleeding -- AA Offset resistance of ink A A Ejection
stability A A
TABLE-US-00017 TABLE 17 Compar- Compar- Compar- Reference ative
ative ative Ink set Example Example 5 Example 6 Example 7 First ink
3-A 3-A 3-A 3-A Surface tension of first 35.2 35.2 35.2 35.2 ink
(mN/m) Second ink None 4-A 5-A 6-A Surface tension of -- 35.5 34.2
35.8 second ink (mN/m) Difference in surface -- 0.3 -1.0 0.6
tension between first and second inks (mN/m) Bleeding -- C AA AA
Offset resistance of ink C C A B Ejection stability A A C C
[0315] As can be seen from the results shown, in the aqueous ink
sets for inkjet recording in the Examples, the occurrence of
bleeding between aqueous inks for inkjet recording and the
occurrence of ink offset were reduced, and the ejection stability
was good.
[0316] In Comparative Examples 1 to 4, the surface tensions were
outside the range of the present invention, and bleeding between
aqueous inks for inkjet recording was found. In the ink set in
Comparative Example 5, a combination of inks containing no
3-methoxybutanol serving as the water-soluble organic solvent (1)
was used, and offset of the inks was observed. In the ink set in
Comparative Example 6, a combination of an ink containing no
glycerin and an ink containing no 3-methoxybutanol was used, and
ejection failure due to drying in the inkjet head portions was
found. In the ink set in Comparative Example 7, a combination of an
ink containing no ethylene urea and an ink containing no
3-methoxybutanol was used, and ejection failure due to drying in
the inkjet head portions was found.
BRIEF DESCRIPTION OF DRAWINGS
[0317] FIG. 1 is a schematic diagram of the microreactor used in
the present invention.
[0318] FIG. 2 illustrates evaluation of bleeding between aqueous
inks for inkjet recording in Examples of the present invention.
REFERENCE SIGNS LIST
[0319] 1: T-shaped micromixer M1
[0320] 2: T-shaped micromixer M2
[0321] 3: T-shaped micromixer M3
[0322] 4: tube reactor R1
[0323] 5: tube reactor R2
[0324] 6: tube reactor R3
[0325] 7: tube reactor P1 for precooling
[0326] 8: tube reactor P2 for precooling
[0327] 9: tube reactor P3 for precooling
[0328] 10: tube reactor P4 for precooling
* * * * *